Help with approval/decline buttons

I have a simple form where I have buttons that attach a copy of the document to an email.  I want a script that replaces the "approve" or "decline" button when it's clicked, with something that says "approved", THEN attaches to the email. Then on the final approval, the entire form becomes read-only.  I am using Pro 2017.

This is a form that will travel along an approval path, until it's approved at the top level.