[Libreoffice-bugs] [Bug 121133] New: Adobe Reader DC claims that the PDF has been modified after signing

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=121133

            Bug ID: 121133
           Summary: Adobe Reader DC claims that the PDF has been modified
                    after signing
           Product: LibreOffice
           Version: 6.1.2.1 release
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: medium
         Component: Printing and PDF export
          Assignee: libreoffice-bugs at lists.freedesktop.org
          Reporter: patrakov at gmail.com

If I sign an existing PDF document in LibreOffice Draw, or export PDF from
LibreOffice Writer and sign it during export, then Adobe Reader does not like
the signature: it claims that the page has been modified. The expectation is
that the signature checking should pass without any complaints.

I will attach an example document signed by LibreOffice Writer.

It is also possible to export the same document without signatures, and then
use the same certificate in jSignPdf 1.6.4 to sign it. The result does not
trigger the "pages modified" alert in Adobe Reader DC, so it is not a problem
with the certificate. I will attach a document to demonstrate this, too.

Note: by default, Adobe Reader DC does not trust certificates issued by COMODO.
To verify my signature, please, in Adobe Reader DC, go to Edit > Preferences >
Signatures > Verification > More... and check the box "Trust ALL root
certificates in the Windows certificate store for: [X] Validating signatures".

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