Stamps on signed PDF Files

Question

I'm trying to understand why "Stamps" can be added and and removed to digitally signed PDF files. The files are to read-only for integity, yet someone could make the PDF look different by simply putting a stamp over something. In addition, if I use a stamp during the signing process, I don't want anyone to be able to remove it.

Is there a different stamping process or tool that can enable stamps to be "locked" into the PDF after being signed?

MikelKlink · Answer

Which changes to a signed PDF are allowed, depends on the certification level of that PDF. The certification level can be set by an initial certification signature on the document, and it can be restricted further by any following signature. The final signer can even lock the document as @try67 described to disallow any further changes (except addition of validation related materials).

For an overview of the certification levels see this Stack Overflow answer.

Thus, in your case the signers all appear to have left the certification level at 3 or default.

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