Speaking of PDF ubiquity -- to which this space is dedicated -- Google's current Google Calendar beta now offers a PDF-based print preview function. Users simply need to open their Google Calendar, navigate to the time period they would like to display and hit the "Print my calendar" button. A PDF will be generated automatically, showing the current calendar sheet.
Once this PDF is saved and opened in Adobe Reader, users can see that the PDF was created using the free iText Java-based PDF creation library.
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.