[Muromec]

>Most PDF readers support these and can verify the signatures using a PKI system similar as is used with HTTPS. Adobe Reader is a popular choice.

One subtle problem in this setup is the trust list. Abode effectively has their own trust bit sovereign rights, while EU has it's own trust list (which doesn't always match with a list of qualified providers as per EU-conforming states). Then US federal government has it's own trust list.

So it's the usual PKI problem.