Comment by jwrallie
I learned that a long time ago when I was a student and wanted to submit a pdf generated by a trial version of some software as an assignment and was trying to be clever and cover the watermark that said unregistered with a white box.
When opening the file in my slow computer, I could see all the rendering of the watermark happening in slow motion until the white box would pop up on top of the text.
When I was a student, and using a shareware or trial version of some software and wanted some printed output from it without a watermark, I printed to postscript (chose a printer that supported postscript and the driver used it instead of rasterized images), but using a file instead of a printer.
I could then open up the postscript, delete the commands that rendered the watermark, save it, then I converted it to PDF so it would be easy to print.