Digital Signatures

Digital signatures are also involve public and private keys but it doesn't work similar to how things work in SSL.

Authenticity and Integrity

It's only used to prove if the message came from a specific sender and the content isn't tampered.

If it's necessary to prove that the message came from a specific sender, then the public key isn't sent in the signature. The public key can be then taken for the sender from a relevant registry.

data isn't encrypted

The actual data itself isn't encrypted. Digital signatures only help to ensure that the data what was generated at source is the same what was received.

digital signature and e-signature aren't same

What we do with adding signatures in PDF are e-signatures. They NOT digital signature.