It seems the Web has gone berserk with denying you access to even browse a site. In some cases, you need to enter a password to appear as a guest. You enter your user ID and password only to find out that the required number of characters exceed the number used for your password of choice. Acrobat can help you manage them.
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.