How to verify a digital signature on a PDF on Linux?

Solution 1:

I spent few hours experimenting with that and found that:

1) pdfsig command from poppler-utils package is able to validate PDF signature. Usage is simple:

pdfsig signed.pdf

But for me it works only for visible signatures (version 0.62.0 on Fedora 28). For invisible signatures it shows:

File 'signed.pdf' does not contain any signatures

2) Master PDF Editor is a GUI tool which shows and validates signatures as shown on the picture below and it is enough to have free version.

3) LibreOffice Draw is able to show and validate signature using File -> Electronic signatures -> Electronic signatures. But in my case it again shows only visible signatures.

Solution 2:

Foxit PhantomPDF should be able to provide the functionality of verifying digital certificates - available on a purchase basis. Foxit Reader can only digitally sign the certificates. mutool sign signed.pdf functionality is not available in ubuntu builds. May be present in Arch.