PDFs with digital signatures can't be converted into PDF/A format

Hello,

Manipulating PDFs that contains digital signature will invalidate the signature, which will cause legal issues in case you need to bring that invoice to court.

Even if you manage to make the conversion work, the PDF signature will have an error saying that the document was altered after it was signed.

Have you checked if the signed PDFs are not already in PDF/A format? In which case a solution could be to detect the signed PDfs, and not convert them (again) in PDF/A.

Hi Radu, To me, the feature is working as designed. If you alter the digitally signed document, the signature is not valid anymore. 

It is the whole purpose of the digital signature; It lets you know that you view the unchanged material. If there are any changes, the error message is shown. 

Yes Timo, I was just explaning that to the Jannik.

Thank you very much for your reply. That makes sense to me.

Thank you for your input, that would actually be a great solution to our problem.

Do you know if there is a way in a workflow to check what format the pdf is in before converting?

Since signed PDFs are not meant to be modified, they often are converted to PDF/A, hence my advice above.

Jannik said:

Do you know if there is a way in a workflow to check what format the pdf is in before converting?

Yes it is possible, but you are asking the wrong question: you should not check if the PDF is in the right format, but if the PDF is signed.

Consider this case: the PDF is signed, but not in PDF/A. If you do the format test, you will detect that it is not in PDF/A, convert it to PDF/A, and destroy the signature.

So to answer the right question: Is there a way in a workflow to check if the PDF is signed before conversion?

Yes, it is possible to configure a workflow to do such a check, but it will need a VAF application containing the code for the signature verification.

Here is an example of signature verification code:
https://stackoverflow.com/questions/39317754/how-to-check-if-a-pdf-file-is-signed-or-not-using-itextsharp-in-c

A PDF library will be needed. I'm not sure signature verification is possible with a free library (many PDF library are paid only, such as iTextSharp in the example I gave you).

Let me know if something is unclear.