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 Feb 28, 2017 at 14:41:33.
(provided by the Example extension).