Seta Bridge Plugins
These are plugins which act as "bridges" between either WooCommerce or Easy Digital Downloads (EDD) and the SetaPDF-Stamper library, which is not licensed for distribution in GPL plugins. SetaPDF-Stamper needs to be purchased separately and installed with the Little Package Stamper plugins for them to stamp.
If you want to watermark and/or encrypt and password your PDFs -- and preserve their internal links and metadata -- these plugins will work for you. Otherwise, if your PDF does not have hyperlinks or other advanced features, WaterWoo or EDDiMark will work fine for you.