Adobe Reader, which I use on MS Windows, has the ability to validate the digital signature (created with an X.509 certificate) in a PDF file.
I'd like to do such verification on Linux desktops. I've tried Evince and Okular, the most recommended PDF readers, but they can't do that. On the other hand, Adobe Reader is not available for Linux (see https://get.adobe.com/reader/otherversions/). PDF readers that are built-in in current versions of Firefox and Chrome neither can verify the signatures.
I'm fine with using a gui, command line tool or a firefox/chrome extension to do this.