How to sign a pdf using openpgp?

Question

Cryptography

Hello!
Such a question - how to sign a pdf file correctly? There are two problems:
1. If you do it raw, that is, just convert the file into a string and sign it - it will naturally become unreadable.
2. If the file is signed 2 times (with another signature) - the first one ceases to be valid (because it has changed)
Where to sign it so that the file remains as if without visible changes, were there all signatures in it? How is this implemented?

Answer 1

you can make a detached signature: gpg -b <подписываемый файл>orgpg -a -b <подписываемый файл>