When creating PDFs from a layout application, you can easily place page numbers on each page. However, when using different producer applications and merging PDF files, you won't have a chance to add page numbers unless they are uniquely added in the right order in each program that produces the PDFs to be merged together.
Add to this any pages that might be downloaded with Web Capture, and you'll quickly find a need to create page numbers after the final PDF has been created.
Create a Button Field.
Select the Form tool from the top level Acrobat toolbar and drag open a rectangle on a page in a PDF file. For the Type, select Button.
Supply a name for the field. In this example I used pageNo for the field name.
In the Field Properties dialog box, click on the Action tab. The default "When this happens" item will be MouseUp. Leave the item selected for MouseUp and click on the Add button.
Note: the code at left will place a page number in the top right corner of each PDF page. To place the page number in a different location, you need to change the coordinates listed between the brackets [...] in the first line of code.
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.