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I am having issues with ClamAV scanning PDF files and reporting back that they are encrypted (and thus cannot be scanned for vulnerabilities). These files don't have a password set on them but do typically have one of the following: a signature annotation added, limited permissions (blocking users from editing certain portions of the file), certified signatures ("Certified by Adobe Sign"), or files that have "Protected View" enabled.

I suspect that this is due to some funny business that Adobe is doing to the file in order to enable these special cases. I'd even bet that Adobe is actually encrypting portions of the file to enable these features.

Can someone explain/confirm that this is the case or explain why ClamAV would claim these files are encrypted?

Chris Williams
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    Are you aware that PDF files can be encrypted using an empty password? For such PDFs Adobe Acrobat opens them without asking the user for a password. Files signed by Adobe Sign, for example, usually are encrypted with an empty user password. – mkl Jun 01 '23 at 21:32

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