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I have already acquired a S/MIME certificate (a .p12 file) issued by an authority. Using it in Writer, I can digitally sign documents by following this procedure : How do I make a digital certificate available to LibreOffice Writer for digital signatures?

Can I do the same for PDF files? If yes, what method do you suggest me? I would prefer a solution that relies on Free Software.

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2 Answers 2

You can sign PDF files with gpg/seahorse.

Learn more: https://help.ubuntu.com/community/GnuPrivacyGuardHowto

You can for instance use OpenSignPDF, that can be download here: http://opensignature.sourceforge.net/english.php

I hope this answers your question.

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Thank you Subv3rsion! Alternatively, I also found some proprietary programs in the Ubuntu Software Center. But I am not going to make advertisement here. –  Agmenor Jun 6 '12 at 17:58
Ok, but please, can you tell me what programs did you found? –  Subv3rsion Jun 6 '12 at 18:02
Note that GPG and Seahorse might not like the S/MIME format that PDF(s) sometimes require in business environments. –  Thomas W. Jun 6 '12 at 18:15
Some times, some people really need to sign with a .p12. This doesn't answer the question. –  jgomo3 Feb 26 '14 at 0:12

PDF Studio 7 Pro, available in the Software Center, features digital signing of PDFs. As of when I am writing it costs only 125 $.

According to the official website, it is indeed S/MIME signing.

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