problem with validation of signature

[vladimír_4743]

We have an electronically stamped document. But when opened in acrobat, the signature is indicated as invalid. The description says that the document was changed after signing. When checked through the DSS (Digital Signature Service), the document and its signature is indicated as valid. What is the solution to this problem? How do we identify where the problem is.

[MikelKlink · Accepted solution]

The problem is the same as explained in this answer and in multiple others here and elsewhere; there is a small error in the original version of the document that usually is ignored by PDF viewers (including Acrobat) but that makes Acrobat reject signatures not covering the full document.

The error is that this initial document revision has a PDF object cross reference table that is split into multiple subsections and has gaps:

xref
0 5
0000000000 65535 f
0000000023 00000 n
0000000252 00000 n
0000000321 00000 n
0000000448 00000 n
6 39
0000000727 00000 n
...

Both aspects are forbidden.

The initial revision of your document claims to be created by Aspose.PDF for .NET 24.11.0; the Aspose PDF components have a long history of producing PDFs with this error. For details see the answer referenced above and more answers referenced from there.