Checking a document with an EDS?

Question

Electronic digital signature

If the user signed the document with his digital signature, how can I check its authenticity?

Answer 1

1. Look who issued the EDS.
2. We look - and whether we trust this issuer.

Answer 2

In the list mentioned by @laxikodeje I will add:
item 3 - if we trust, we check the validity of the signature.
note to paragraph 2 - in the Russian Federation there is a list of Certification Centers, which everyone (presumably - subjects, but in general - everyone) must trust. In addition, CAs can trust other CAs, so everything is like the girls in VK "everything is complicated."