By default, Adobe Acrobat allows users to place various standard stamps on your documents such as 'Approved', 'Declined' or 'Accepted'. That said, you can also create your own custom stamps. Using this option, you can take a logo or other image from another application and turn it into a custom stamp. Once created, you can apply it to any PDF document in Acrobat.
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.