Stamping text and images in PDF files has been one of most often requested feature additions to Acrobat over the past few years - it has arrived with Acrobat 6 (Standard and Professional). Acrobat Professional users can now apply them in batches by using the Batch Processing tool.
The ability to add header & footer text-based info will be welcomed by users, making it easy to add text information like page numbers, date and author information.
The beauty of the PDF-based watermarks & backgrounds is that they can contain any combination of text and images - allowing a user to add visually rich content underneath or above any page.
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.