So when I download a freebie or purchase a D&D/OSR/RPG PDF, I generally take it to my friendly local small independant print shop where the absolute dear of an owner uses an Acrobat plug-in to output the PDF in booklet format (although lately I've been handling the mouse-clicks) which is than printed, folded, and stapled into assembled booklet form by the absolute behemoth of a printer in the back.
However, whenever I've tried that with a purchased or free watermarked PDF, the plug-in is denied permission to output in booklet format. Which kind of defeats the purpose of exporting the file into an easy to read, store and use format (with the amount of reality TV that The Warden watches on MY computer, referencing the file on the computer is not a practical option, nevermind that I HATE using a computer while DMing).
So yeah, watermarking PDFs, please don't waste my time with that jive...and I seriously doubt it is going to help you make a living with your hobby publishing venture. Considering that EDIT 95%+ of purchased PDFs I own don't have watermarks, it really makes you look like a worried dork.
My Watermark is integrity and dedication to supporting the publishers that produce material that I use, there's no way that I'm going to be part of cash-blocking any of the awesome dudes out there in OSR publishing land!