Vocal Creative Commons evangelist Cory Doctorow has been in the news lately, celebrating both his novel's 4th consecutive list on the New York Times Bestseller List and the release of a new graphic novel based on his short stories.
"So, what's the PDF angle here?" I hear you cry. Well, both have been licensed using the Creative Commons system, which allows content authors to creatively license and protect their content. According to the Creative Commons website:
Share, Remix, Reuse -- Legally
Creative Commons provides free tools that let authors, scientists, artists, and educators easily mark their creative work with the freedoms they want it to carry. You can use CC to change your copyright terms from "All Rights Reserved" to "Some Rights Reserved."
The basic upshot is that for the Doctorow works in question, you can simply download PDF versions of them, subject to their particular copyright restrictions, of course!
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.