The Flatten document tool allows you to dramatically reduce the size of certain PDF files by flattening active parts within the document, like navigation buttons and forms. It is also possible to remove extraneous mark-up from your document, or for example, to flatten form data into the main document content so making the completed form viewable across many platforms.
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.