With this plug-in you can digitally sign PDF files using the standard digital signature capabilities that were introduced with Acrobat 4.0. You can also create secure documents using Entrust® recipient lists for targeted, secure document distribution. Documents are encrypted using standard Acrobat 40-bit RC4 encryption. This Plug-In requires the Entrust/Entelligence (tm) 4.0 or later client.
OK, so you want to stamp your document. Maybe you need to give reviewers some advice about the document's status or sensitivity. This tip from author Ted Padova demonstrates how to add stamps with the Stamp Tool along with related comments.