Hello,
this message comes from the new Outlook. PDF24 Creator supports the new Outlook since version 11.28.0, with the email interface "Outlook New".
- Update PDF24 Creator to the latest version: https://tools.pdf24.org/en/creator
- Open the PDF24 Settings (PDF24 icon in the notification area of the taskbar › Settings).
- On the page "Email Interface" choose "Outlook New".
Then send the PDF again. With "Outlook New", PDF24 hands the email over as an EML file, so your Outlook signature is not added automatically.
If the attachments are still empty after that, please let us know here.