{"id":66928,"date":"2026-11-11T20:47:49","date_gmt":"2026-11-11T20:47:49","guid":{"rendered":"https:\/\/help.pdf24.org\/en\/sign-pdf\/"},"modified":"2026-11-12T00:08:59","modified_gmt":"2026-11-12T00:08:59","slug":"sign-pdf","status":"publish","type":"post","link":"https:\/\/help.pdf24.org\/en\/sign-pdf\/","title":{"rendered":"Sign PDF: insert your signature and sign digitally"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">Want to sign a PDF without printing and scanning it? With PDF24 you place your signature on the page in a few steps, online or offline. If you need to, you can also sign the PDF digitally with a certificate.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">These are two different things, and both are often called a \"signature\". This guide explains both, shows how to verify a signature and helps with the most common problems.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Contents<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"#difference\">Signature image or digital signature: which one do I need?<\/a><\/li>\n\n\n<li><a href=\"#online\">Insert a signature into a PDF (online)<\/a><\/li>\n\n\n<li><a href=\"#toolbox\">Insert a signature in the PDF24 Toolbox (offline)<\/a><\/li>\n\n\n<li><a href=\"#many-pages\">The same signature on many pages or in many files<\/a><\/li>\n\n\n<li><a href=\"#forms\">Fill out and sign PDF forms<\/a><\/li>\n\n\n<li><a href=\"#several-people\">Several people sign one PDF<\/a><\/li>\n\n\n<li><a href=\"#digital-online\">Sign a PDF digitally (online)<\/a><\/li>\n\n\n<li><a href=\"#digital-creator\">Sign a PDF with a certificate in PDF24 Creator (offline)<\/a><\/li>\n\n\n<li><a href=\"#timestamp\">Timestamps and validation data (LTV)<\/a><\/li>\n\n\n<li><a href=\"#verify\">Verify a digital signature<\/a><\/li>\n\n\n<li><a href=\"#invalid\">Why does a signature become invalid after a change?<\/a><\/li>\n\n\n<li><a href=\"#qes\">Qualified electronic signature (QES): can PDF24 do it?<\/a><\/li>\n\n\n<li><a href=\"#problems\">Common problems and solutions<\/a><\/li>\n\n<\/ul>\n\n\n\n<h2 id=\"difference\" class=\"wp-block-heading\">Signature image or digital signature: which one do I need?<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Visible signature:<\/strong> your signature appears as an image on the page, just like one made with a pen. You draw it, type your name or use a photo or scan. No certificate is needed. It does not prove who added it, though, and the PDF can be changed afterwards without anyone noticing.<\/li>\n\n\n<li><strong>Digital signature (with a certificate):<\/strong> a cryptographic seal inside the PDF. It shows which certificate was used and makes every later change detectable. Nothing has to be visible on the page, but it can carry a signature image as well. You need a certificate for it.<\/li>\n\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">You can combine both: insert the visible signature first, then sign the finished PDF digitally as the last step.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Which PDF24 tool does what:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Online, <a href=\"https:\/\/tools.pdf24.org\/en\/sign-pdf\">Sign PDF<\/a>:<\/strong> visible signature (type, draw, image, camera) and digital signature, in the browser on any device.<\/li>\n\n\n<li><strong>PDF24 Toolbox (Windows, offline), \"Sign PDF\":<\/strong> visible signature (draw, image, camera).<\/li>\n\n\n<li><strong>PDF24 Creator (Windows, offline), when saving as PDF:<\/strong> digital signature with a certificate from Windows, optionally with a timestamp. No visible signature image.<\/li>\n\n\n<li><strong>Verify:<\/strong> online with <a href=\"https:\/\/tools.pdf24.org\/en\/verify-pdf-signatures\">Verify PDF signatures<\/a>, offline in PDF24 Reader in the \"Signatures\" sidebar.<\/li>\n\n<\/ul>\n\n\n\n<h2 id=\"online\" class=\"wp-block-heading\">Insert a signature into a PDF (online)<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Open <a href=\"https:\/\/tools.pdf24.org\/en\/sign-pdf\">Sign PDF<\/a> and choose your PDF with \"Choose file\", or drag it into the file box. The PDF opens in the editor.<\/li>\n\n\n<li>Click \"Insert signature\" in the toolbar. Or right-click the spot on the page and choose \"Sign here\".<\/li>\n\n\n<li>The first time, create your signature: \"+ New signature\", then one of the four ways (see below).<\/li>\n\n\n<li>Click your saved signature. It appears on the page. Drag it to the right spot and drag its corners until the size fits.<\/li>\n\n\n<li>If needed, add more with \"Insert\", for example place and date as text.<\/li>\n\n\n<li>Click \"Save PDF\". The signed PDF is downloaded.<\/li>\n\n<\/ol>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"838\" height=\"809\" src=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-choose-signature.png\" alt=\"The &quot;Choose signature&quot; window with the tabs &quot;Type&quot;, &quot;Draw&quot;, &quot;Upload image&quot; and &quot;Camera&quot;; a typed name in several fonts\" class=\"wp-image-67040\" srcset=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-choose-signature.png 838w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-choose-signature-300x290.png 300w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-choose-signature-768x741.png 768w\" sizes=\"auto, (max-width: 838px) 100vw, 838px\" \/><figcaption class=\"wp-element-caption\">Type, draw, upload or photograph a new signature<\/figcaption><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Four ways to create your signature<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\"Type\":<\/strong> enter your name in the field \"Your name\", pick one of the handwriting fonts, choose Black or Blue under \"Color\", then \"Apply\".<\/li>\n\n\n<li><strong>\"Draw\":<\/strong> sign in the field with the mouse, touchpad, pen or finger, then \"Apply\". \"Clear\" empties the field.<\/li>\n\n\n<li><strong>\"Upload image\":<\/strong> \"Select file\u2026\" and choose a photo or scan of your signature. The \"White threshold\" slider removes the paper, \"Black\" makes the ink black. Then \"Use\".<\/li>\n\n\n<li><strong>\"Camera\":<\/strong> sign a white sheet of paper, click \"Activate Camera\", hold the sheet in front of the camera and click \"Take Photo\". On a smartphone this is often the quickest way.<\/li>\n\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Good to know<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Change the color afterwards:<\/strong> click the inserted signature. In the small bar above it, choose black, blue or \"Custom color\u2026\" and the \"Opacity\". This also works for uploaded and photographed signatures; white paper becomes transparent.<\/li>\n\n\n<li><strong>Saved signatures<\/strong> are kept only in your browser on this device, not on our server. In another browser, a private window or after clearing the browser data they are not there. Simply create them again. To remove a signature from the list, click \"Delete\".<\/li>\n\n\n<li><strong>Size:<\/strong> once you have made a saved signature larger or smaller, it is inserted at that size the next time.<\/li>\n\n\n<li><strong>Privacy:<\/strong> to save it, the PDF is transferred encrypted to our servers in Germany and deleted automatically after one hour.<\/li>\n\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Besides your signature you can insert text, check marks, images and stamps in the editor. How to add text, cover spots or redact content is explained on the page <a href=\"https:\/\/help.pdf24.org\/en\/edit-pdf-with-pdf24\/\">Edit PDF with PDF24<\/a>.<\/p>\n\n\n\n<h2 id=\"toolbox\" class=\"wp-block-heading\">Insert a signature in the PDF24 Toolbox (offline)<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">With the free <a href=\"https:\/\/tools.pdf24.org\/en\/creator\">PDF24 Creator<\/a> for Windows you sign without the internet. Your files never leave your computer.<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Open the PDF24 Toolbox and then \"Sign PDF\".<\/li>\n\n\n<li>Choose <strong>the PDF first<\/strong> with \"Choose file\" or drag it into the window.<\/li>\n\n\n<li>Click the pen icon \"Add a signature\" in the toolbar.<\/li>\n\n\n<li>The first time, the window for creating a signature opens right away: \"Draw\", \"Upload\" (an image of your signature) or \"Camera\". A drawn signature is taken over with the green check mark (\"Add signature\"). Once a signature is saved, you add more with the plus icon \"Add new signature\".<\/li>\n\n\n<li>Click your signature to add it to the document. Move it and adjust its size.<\/li>\n\n\n<li>With \"Add text\" and \"Add picture\" you add, for example, a date or a stamp.<\/li>\n\n\n<li>Click \"Create PDF\" and save the result. The new file has the name of the original plus \"_signed\"; your original stays unchanged.<\/li>\n\n<\/ol>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"620\" src=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-toolbox-saved-signatures.png\" alt=\"The PDF24 Toolbox, &quot;Sign PDF&quot; with an open PDF and the window with the saved signatures\" class=\"wp-image-67041\" srcset=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-toolbox-saved-signatures.png 1024w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-toolbox-saved-signatures-300x182.png 300w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-toolbox-saved-signatures-768x465.png 768w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">Click a saved signature to add it to the document<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Good to know:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The Toolbox remembers the size at which you last used a saved signature.<\/li>\n\n\n<li>Paste an image from the clipboard with Ctrl+V.<\/li>\n\n\n<li>Prepare an uploaded signature in the preview: \"Modify white threshold\" removes the paper, \"Black\" makes the ink black.<\/li>\n\n\n<li>This Toolbox tool has no typing and no digital signing. To sign digitally offline, use <a href=\"#digital-creator\">saving in PDF24 Creator<\/a>.<\/li>\n\n<\/ul>\n\n\n\n<h2 id=\"many-pages\" class=\"wp-block-heading\">The same signature on many pages or in many files<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">If every page needs initials or a signature, place it only once online:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Insert the signature on the first page and move it to the right spot.<\/li>\n\n\n<li>Click it and choose \"Copy to pages\" in the bar above it.<\/li>\n\n\n<li>All other pages are already entered. You can change this, e.g. \"2-4, 6\". Click \"Insert\".<\/li>\n\n\n<li>Save with \"Save PDF\".<\/li>\n\n<\/ol>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"830\" height=\"255\" src=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-bar-copy-to-pages.png\" alt=\"The bar of a selected signature with color dots, an opacity slider and the &quot;Copy to pages&quot; icon (marked)\" class=\"wp-image-67042\" srcset=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-bar-copy-to-pages.png 830w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-bar-copy-to-pages-300x92.png 300w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-bar-copy-to-pages-768x236.png 768w\" sizes=\"auto, (max-width: 830px) 100vw, 830px\" \/><figcaption class=\"wp-element-caption\">\"Copy to pages\" puts the same signature on further pages<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">In the Toolbox you place the signature on each page separately. When you sign many files one after another, it helps that online and in the Toolbox your saved signature keeps the size you used last.<\/p>\n\n\n\n<h2 id=\"forms\" class=\"wp-block-heading\">Fill out and sign PDF forms<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Open the form with <a href=\"https:\/\/tools.pdf24.org\/en\/fill-out-pdf\">Fill out PDF<\/a>.<\/li>\n\n\n<li>Fill in the fields. If the form has a signature field, click it and choose your signature. It is placed in the field.<\/li>\n\n\n<li>If the form has no signature field or no fillable fields at all, switch to the mode \"Insert\" at the top and place text, check marks and your signature freely on the page.<\/li>\n\n\n<li>Click \"Save PDF\".<\/li>\n\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">If nobody should be able to change the entries afterwards, flatten the form, for example with <a href=\"https:\/\/tools.pdf24.org\/en\/flatten-pdf\">Flatten PDF<\/a>. If you also want to sign the form digitally, do that at the very end.<\/p>\n\n\n\n<h2 id=\"several-people\" class=\"wp-block-heading\">Several people sign one PDF<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Visible signatures:<\/strong> the PDF goes round. Each person opens the file they received, inserts their signature, saves and passes the new file on. Always continue with the most recently saved file, otherwise earlier signatures are missing. If everyone uses the same device, each person creates their own signature and places it in their spot.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Digital signatures:<\/strong> the online editor writes the file anew when saving. A signature that is already in the PDF is then no longer valid. Several digital signatures one after another, where the first one stays valid, are therefore not possible online. So collect all visible signatures first; the digital signature comes last.<\/p>\n\n\n\n<h2 id=\"digital-online\" class=\"wp-block-heading\">Sign a PDF digitally (online)<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Open <a href=\"https:\/\/tools.pdf24.org\/en\/sign-pdf\">Sign PDF<\/a> and choose your PDF.<\/li>\n\n\n<li>In the menu at the top, switch the mode from \"Insert\" to \"Sign\".<\/li>\n\n\n<li>With \"Choose signature\u2026\" pick a signature image and click the page to place it. Or tick \"Sign without a visible signature\".<\/li>\n\n\n<li>Under \"Certificate\" choose:\n\n<ul class=\"wp-block-list\">\n<li><strong>\"PDF24 certificate (self-signed)\":<\/strong> no certificate of your own needed. The signature makes later changes detectable but does not confirm who you are. PDF programs show it as not verified.<\/li>\n\n\n<li><strong>\"Sign in the browser (key stays local)\":<\/strong> with your own certificate file (.p12 or .pfx). Choose it with \"Choose certificate file\u2026\" and enter the \"Certificate password\". The certificate file and the key never leave your device.<\/li>\n\n<\/ul>\n<\/li>\n\n\n<li>Optionally tick \"Request a timestamp (TSA)\" and choose a service (DigiCert, Sectigo or GlobalSign), and fill in \"Name\", \"Reason\" (e.g. \"I agree to the terms defined by this document\" or \"Custom reason \u2026\") and \"Location\".<\/li>\n\n\n<li>\"The document will be digitally signed on save.\" appears. Click \"Save PDF\".<\/li>\n\n<\/ol>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"810\" height=\"632\" src=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-sign-mode.png\" alt=\"The editor in the &quot;Sign&quot; mode with &quot;Choose signature\u2026&quot;, &quot;Certificate&quot;, &quot;Request a timestamp (TSA)&quot;, &quot;Name&quot;, &quot;Reason&quot; and &quot;Location&quot;\" class=\"wp-image-67043\" srcset=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-sign-mode.png 810w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-sign-mode-300x234.png 300w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-sign-mode-768x599.png 768w\" sizes=\"auto, (max-width: 810px) 100vw, 810px\" \/><figcaption class=\"wp-element-caption\">The settings for the digital signature in the \"Sign\" mode<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Good to know:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>One signature is added per save. Make all other changes first.<\/li>\n\n\n<li>The visible signature shows only your signature image. Name, reason, location and time are in the signature details, which PDF programs show when you click the signature.<\/li>\n\n\n<li>With \"Save settings for this signature\" the browser remembers certificate, timestamp, name, reason and location for that signature. The password is never stored.<\/li>\n\n\n<li>Certificates on a smart card or USB token cannot be used in the browser. Use <a href=\"#digital-creator\">PDF24 Creator<\/a> for them.<\/li>\n\n<\/ul>\n\n\n\n<h2 id=\"digital-creator\" class=\"wp-block-heading\">Sign a PDF with a certificate in PDF24 Creator (offline)<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">PDF24 Creator signs when saving as PDF, with a certificate from the Windows certificate store. This also works with certificates on smart cards or tokens if the card software makes them available there.<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Open the save dialog:\n\n<ul class=\"wp-block-list\">\n<li><strong>New document:<\/strong> print it to the printer \"PDF24\". In the PDF24 Assistant click \"Save as...\" and, if a small menu appears, \"Selected file\". The dialog \"Format properties\" opens.<\/li>\n\n\n<li><strong>Existing PDF:<\/strong> drag it into PDF24 Creator, choose \"Save as...\" for the document and the profile \"Custom\".<\/li>\n\n<\/ul>\n<\/li>\n\n\n<li>In the dialog, choose \"Signature\" under \"PDF\" on the left.<\/li>\n\n\n<li>Tick \"Use signature\".<\/li>\n\n\n<li>Click \"Choose Certificate\" and select your certificate.<\/li>\n\n\n<li>Optionally: \"Reason\" (\"I am the author of the document\", \"I sign the document\", \"I have seen the document\") or \"Other Reason\", \"Location\", \"Timestamp service\" and \"Embed validation data (LTV)\".<\/li>\n\n\n<li>Click \"Continue\" and choose the name and folder of the file.<\/li>\n\n<\/ol>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"885\" height=\"592\" src=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-assistant-signature.png\" alt=\"The Assistant dialog, page PDF \u203a &quot;Signature&quot; with &quot;Use signature&quot;, &quot;Choose Certificate&quot;, &quot;Reason&quot;, &quot;Location&quot; and &quot;Timestamp service&quot;\" class=\"wp-image-67044\" srcset=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-assistant-signature.png 885w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-assistant-signature-300x201.png 300w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-assistant-signature-768x514.png 768w\" sizes=\"auto, (max-width: 885px) 100vw, 885px\" \/><figcaption class=\"wp-element-caption\">The settings for the digital signature in the PDF24 Assistant<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Good to know:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>No certificate?<\/strong> \"Create self signed certificate\" (link in the dialog or in the menu of PDF24 Creator) creates one. It is fine for testing or for recipients who know your certificate. \"Manage certificates\" opens the Windows certificate manager.<\/li>\n\n\n<li><strong>Always sign the same way:<\/strong> create a profile with your signature under \"Output profiles\" and choose it when saving.<\/li>\n\n\n<li><strong>Signature and password protection<\/strong> can be combined in the same dialog (page \"Security\"). Since version 11.32.0 the file is encrypted and validly signed in one step.<\/li>\n\n\n<li><strong>If signing fails<\/strong>, for example because the timestamp service cannot be reached, PDF24 shows \"The PDF file could not be signed.\" with the reason and asks \"Save the file without a signature?\". With \"No\" nothing is saved.<\/li>\n\n\n<li><strong>Visible and digital:<\/strong> PDF24 Creator does not add a signature image. Insert your signature first with \"Sign PDF\", then sign the finished file when saving.<\/li>\n\n<\/ul>\n\n\n\n<h2 id=\"timestamp\" class=\"wp-block-heading\">Timestamps and validation data (LTV)<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Without a timestamp<\/strong> the signing time comes from the clock of the computer where the PDF was signed. Adobe Acrobat says \"The time of signature is determined based on the time on the signer's computer.\", and checking tools report that the time is not confirmed.<\/li>\n\n\n<li><strong>With a timestamp<\/strong> a timestamp service confirms when the PDF was signed. PDF24 offers DigiCert, Sectigo and GlobalSign, PDF24 Creator also FreeTSA and a custom URL. An internet connection is needed for this.<\/li>\n\n\n<li><strong>Validation data (LTV)<\/strong> (PDF24 Creator only) puts the answers of the certification authorities, confirming that your certificate was not revoked, into the PDF. This keeps the signature verifiable later, even after the certificate has expired. It is useful above all for documents that are kept for a long time.<\/li>\n\n<\/ul>\n\n\n\n<h2 id=\"verify\" class=\"wp-block-heading\">Verify a digital signature<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Online<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Open <a href=\"https:\/\/tools.pdf24.org\/en\/verify-pdf-signatures\">Verify PDF signatures<\/a> and choose one or more signed PDFs.<\/li>\n\n\n<li>For every signature you see who signed and when, whether the document was changed afterwards and whether the signer is confirmed by a recognised authority.<\/li>\n\n\n<li>\"Check revocation online\" asks the certification authority whether a certificate was revoked. \"Report as PDF\" saves the result, e.g. for your records.<\/li>\n\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">Typical results:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\"Signature valid \u2013 the document is unchanged since signing\": everything is fine.<\/li>\n\n\n<li>\"Signature valid \u2013 the document was changed afterwards (a later version)\": the signature itself is intact, but something was added later, for example filled-in fields or comments. \"Details\" shows what was changed. \"Open signed version\" shows the document exactly as it was signed.<\/li>\n\n\n<li>\"Signature invalid \u2013 the signed content was changed\": the file was changed after signing. Ask the sender for a new signed version.<\/li>\n\n\n<li>\"Signer not confirmed: the certificate is self-signed - anyone can make one under any name\": the file is unchanged, but the identity is not confirmed.<\/li>\n\n\n<li>\"Qualified electronic signature (eIDAS)\": the certificate comes from a qualified trust service on the EU trust list.<\/li>\n\n<\/ul>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"1180\" height=\"305\" src=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-verify-signatures.png\" alt=\"Result of &quot;Verify PDF signatures&quot;: &quot;Signature valid \u2013 the document is unchanged since signing&quot;, the signer with timestamp and the note on the self-signed certificate\" class=\"wp-image-67045\" srcset=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-verify-signatures.png 1180w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-verify-signatures-300x78.png 300w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-verify-signatures-1024x265.png 1024w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-verify-signatures-768x199.png 768w\" sizes=\"auto, (max-width: 1180px) 100vw, 1180px\" \/><figcaption class=\"wp-element-caption\">Check result of a signature with the PDF24 certificate and a timestamp<\/figcaption><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Offline in PDF24 Reader<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Open the PDF in PDF24 Reader and click \"Signatures\" in the sidebar. The list shows every signature with signer and date, and a colored dot shows its state, e.g. \"Valid \u2013 trusted certificate\", \"Valid \u2013 untrusted certificate\" or \"Invalid \u2013 document modified\". Click a signature to see the details, such as \"The document has not been modified since signing\" or \"Signing time verified by timestamp\". Whether a certificate is trusted is decided by the Windows certificate store.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"570\" src=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-reader-signatures.png\" alt=\"PDF24 Reader with the &quot;Signatures&quot; sidebar: a signature selected, below it status, signer, location, reason and the timestamp\" class=\"wp-image-67046\" srcset=\"https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-reader-signatures.png 1024w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-reader-signatures-300x167.png 300w, https:\/\/help.pdf24.org\/en\/wp-content\/uploads\/sites\/3\/2026\/11\/sign-pdf-reader-signatures-768x428.png 768w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">PDF24 Reader shows the details of each signature<\/figcaption><\/figure>\n\n\n\n<h2 id=\"invalid\" class=\"wp-block-heading\">Why does a signature become invalid after a change?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">When signing, a checksum is calculated from the content of the file and sealed with your certificate. If even one character changes afterwards, the checksum no longer matches and the signature counts as invalid. That is exactly its purpose.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This happens, for example, when editing, merging, compressing, rotating or removing pages, converting to PDF\/A and when saving again in another program. So:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Signing is always the last step.<\/strong> Edit, fill in, merge and compress first, then sign.<\/li>\n\n\n<li><strong>Don't edit a signed PDF.<\/strong> If you need a changed version, change your unsigned original and sign it again. For a PDF from someone else, ask the sender for a new version.<\/li>\n\n\n<li><strong>Merging signed PDFs:<\/strong> the signatures of the individual files are no longer valid afterwards. Better send signed documents as separate files (more under <a href=\"https:\/\/help.pdf24.org\/en\/how-to-merge-pdf-files-with-pdf24\/#was-passiert\">Merge PDF: what happens when merging?<\/a>).<\/li>\n\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Some programs append later changes to the file instead of writing it anew (for example filled-in form fields or another signature). Then the first signature stays valid, and the check says \"the document was changed afterwards\". The PDF24 online editor, in contrast, writes the file anew when saving.<\/p>\n\n\n\n<h2 id=\"qes\" class=\"wp-block-heading\">Qualified electronic signature (QES): can PDF24 do it?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">In the EU, the eIDAS regulation distinguishes three levels of electronic signature:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Simple electronic signature:<\/strong> e.g. an inserted signature image or a typed name.<\/li>\n\n\n<li><strong>Advanced electronic signature:<\/strong> a digital signature that is uniquely linked to one person and makes changes detectable.<\/li>\n\n\n<li><strong>Qualified electronic signature (QES):<\/strong> an advanced signature with a qualified certificate from a trust service provider, created with a secure signature creation device, such as a signature card or the provider's remote signing service.<\/li>\n\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Which form your document needs, the recipient or a legal adviser can tell you.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">What PDF24 can do here:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>PDF24 does not issue certificates.<\/strong> A qualified certificate is only available from a trust service provider.<\/li>\n\n\n<li><strong>Online<\/strong> a QES is not possible: the key of a QES is on a signature card or with the provider and cannot be used as a .p12 file.<\/li>\n\n\n<li><strong>In PDF24 Creator<\/strong> you sign with certificates from the Windows certificate store, including smart cards. Whether the result is a QES depends only on your certificate and your signature card, not on the program. Check the first file you sign this way with <a href=\"https:\/\/tools.pdf24.org\/en\/verify-pdf-signatures\">Verify PDF signatures<\/a>. For a QES it shows \"Qualified electronic signature (eIDAS)\".<\/li>\n\n\n<li><strong>Verifying<\/strong> a QES works online: the tool checks the certificates against the EU trust list.<\/li>\n\n<\/ul>\n\n\n\n<h2 id=\"problems\" class=\"wp-block-heading\">Common problems and solutions<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">\"This file type is not possible here. Allowed: PDF\" (Toolbox)<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">You chose the image of your signature first in the Toolbox. Choose the PDF first and add the signature afterwards with the pen icon.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">The signature has a white or grey box<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">When uploading or photographing, move the \"White threshold\" slider (Toolbox: \"Modify white threshold\") until the paper disappears. Online you can also click the signature and recolor it; white paper becomes transparent. It works best with a dark pen on white paper in good light.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">My saved signature is gone \/ missing on the other PC<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Saved signatures are kept in the browser (online) or in the PDF24 Toolbox on this computer. Other browsers, private windows, cleared browser data or another PC don't know them, and there is no export function. Create the signature there again, fastest with \"Camera\" or a photo of your signature.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">The signature should be blue<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Online: when typing, choose Blue under \"Color\", or click the inserted signature and choose blue or \"Custom color\u2026\" in the bar.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Adobe shows \"identity unknown\" or \"not trusted\"<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The signature was made with a self-signed certificate (the PDF24 certificate or one you created yourself). The file is still protected against changes; only the signer is not confirmed. For a confirmed identity you need a certificate from a recognised certification authority, or the recipient marks your certificate as trusted on their side.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Adobe says the signing time comes from the signer's computer<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The signature has no timestamp. Sign with \"Request a timestamp (TSA)\" (online) or with a \"Timestamp service\" (PDF24 Creator). See <a href=\"#timestamp\">Timestamps<\/a>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">The signature is invalid after editing, merging or compressing<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">That is intended, see <a href=\"#invalid\">Why does a signature become invalid?<\/a>. Sign again as the last step.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Signing with a smart card: \"Error while acquireing certificates private key\"<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Older versions of PDF24 Creator opened the key only through the older Windows interface, which many smart card programs no longer offer. Update to the current version: <a href=\"https:\/\/tools.pdf24.org\/en\/creator\">PDF24 Creator<\/a>. Also check that the software of your card is installed and the certificate appears under \"Manage certificates\".<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">A signature with password protection was shown as faulty<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A bug in older versions: signature and password protection in the same profile produced an invalid signature. This is fixed since version 11.32.0. Please update PDF24 Creator.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">\"Signing in the browser failed \u2013 check certificate and password.\"<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Online, the password does not match the certificate file, or the file is not a .p12\/.pfx with a private key. If needed, export the certificate again including the private key.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">The signed PDF is not in my e-mail attachment<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">PDF24 always saves a new file; the original stays unchanged. If you signed an attachment from Outlook, attach the new, signed file to your reply.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">I want to remove a signature<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A digital signature is meant to show that a document has not changed since it was signed. If you signed it yourself, simply use your unsigned original file. If you need an unsigned version of someone else's PDF, ask the sender.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">If a feature is missing or something does not work, write to us at team@pdf24.org.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Sign a PDF with PDF24: draw, type or upload your signature, online or offline. Plus: sign digitally with a certificate and verify PDF signatures.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2,4],"tags":[],"class_list":["post-66928","post","type-post","status-publish","format-standard","hentry","category-creator","category-online-tools"],"_links":{"self":[{"href":"https:\/\/help.pdf24.org\/en\/wp-json\/wp\/v2\/posts\/66928","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/help.pdf24.org\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/help.pdf24.org\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/help.pdf24.org\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/help.pdf24.org\/en\/wp-json\/wp\/v2\/comments?post=66928"}],"version-history":[{"count":1,"href":"https:\/\/help.pdf24.org\/en\/wp-json\/wp\/v2\/posts\/66928\/revisions"}],"predecessor-version":[{"id":67047,"href":"https:\/\/help.pdf24.org\/en\/wp-json\/wp\/v2\/posts\/66928\/revisions\/67047"}],"wp:attachment":[{"href":"https:\/\/help.pdf24.org\/en\/wp-json\/wp\/v2\/media?parent=66928"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/help.pdf24.org\/en\/wp-json\/wp\/v2\/categories?post=66928"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/help.pdf24.org\/en\/wp-json\/wp\/v2\/tags?post=66928"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}