c42pdf is a tiny and fast tool to convert TIFF CCITT4-compressed images
(typical black-and-white scanner output) to PDF rapidly. Users include
document delivery services, public libraries etc. It handles multipage
TIFF and is able to do some simple resizing/cropping/rotating. It is
built on Thomas Merz' PDFLIB and thus inherits its Aladdin Free Public License which allows you to use, modify the source and redistribute it for free, only that there are restrictions in selling the program itself to third parties (but there are no restrictions at all on commercial usage of the program).
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.