Massive quality loss after using the option to black PDF files

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    I have been using PDF24 for quite some time now, and I am more than happy that I can have most of the tools I need in my everyday life in one singular application.

    Recently, I have had the need to black-out some sensitive information from PDF files. Thankfully, PDF24 provides a solution for that as well.

    Sadly, when using the tool, the quality of the document greatly decreases which makes it hard for to be read or printed out.

    I have tried changing up some profile settings which brought no change whatsoever.

    I was hoping to find a resolution to this issue here.

    Thank you.

    Stefan Ziegler

    The blacken PDF Tool renders modified pages to an image and embeds that image back into the PDF. The quality decreases by this step but the page should still be readable. Can you send me a screenshot or the PDF files to so that I can have a look?


    Hi there.
    I have the same issue. Blacken PDF Tool decreases quality significantly.
    Although it's still easily readable for me, older people have problems with reading the content of printed documents. Fonts gets a little too blurry for them.
    Having an option to increase quality even at the cost of file size would be great.

    Stefan Ziegler

    There is a setting option with the name "blackenSecurity.dpi". Here you can set the DPI value that is used for blackening. The default value is 150. This value can be created as a DWORD in the registry path HKLM\SOFTWARE\PDF24 or HKCU\SOFTWARE\PDF24.

    The option is described in the manual:

    If you increase the DPI value, the quality of the page should improve, but this will also increase the file size. A lower value results in lower quality and a smaller file size.

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