Adobe PDF supports embedded digital signatures since at least version 1.7
These are viewable, and optionally manipulable, in the free Acroread products.
It would be nice to be able to at least view and verify certificates in products built with Poppler, so as to allow e.g. scripted verification of a document repository.
*** This bug has been marked as a duplicate of bug 16770 ***
on Dec 11, 2016 at 09:55:17.
(provided by the Example extension).