One way to keep your static PDF documents relevant is to create web links to "live" websites that are regularly updated with the latest information. In fact, the process is even easier than creating web links in HTML!
In Acrobat, simply:
Select the Link Tool (Tools > Advanced Editing > Link Tool).
Drag the appropriate area of the page to create your link.
Choose 'Open a web page'.
Enter the web address (e.g. http://www.planetpdf.com/) and click OK.
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.