How the chatter post are created when a document is Send for Signature using conga and adobe sign

I want to know how the chatter post are created when a document is send for signature and after that the cmments are generated in that post if the mail is undelivered or when the document is signed.

The comment in chatter posts are generated automatically by a user  eg "ABC" commented on your post, so I want to change this user who will comment on the post. Please guide me how can this be implemented.

All the adobe sign chatter settings are enable for the org, like "Post when recipient email bounces", "Post when agreement transactions done" etc...