Digital signatures attached to the file

Question

I need to implement digital signatures to my web app. I followed this and this example, and have successfully signed and verified given file.

My questions are regarding the flow:

1. I can export the signature, so what should I do with the signature? Save it in the database?
2. If I attach signature to the file using BouncyCastle exported file is not readable. Should file with attached signature be readable?
3. Is this the correct flow of digital signature: create the signature with user's certificate, store the signature, create endpoint for signature verification?
4. If 3. is correct, does that mean if the file is sent outside an app, recipient wouldn't know if the file is signed? Should the signature be attached to the file? If yes, is there solution for all types of files (ie. I have found pdf based solutions).

Maybe the question is to broad, but I am open to any material regarding the subject.

Answer 1

A valid digital signature gives a recipient reason to believe that the message was created by a known sender (authentication), that the sender cannot deny having sent the message (non-repudiation), and that the message was not altered in transit (integrity)

More info : http://javaint4bytes.blogspot.com/2018/04/java-signature-certificates.html