STDU Converter is easy to use application for convert DjVu and TIFF files to PDF. You need only select your DjVu file and push button "Convert". You can select pages which you want to convert. You can rotate some pages, if you need. You can create your own tree of content in the result's document.
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.