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.