I'm assuming you've already gone through the 30-day trial of full functionality without the watermark being present first. (What we refer to as "the 30-day trial")
If you haven't, you need to get a trial licence through the wizard.

If you've already gone through those 30 days, then you need to buy a full licence to get rid of the watermark.
PTC Marketer for Creo and Mathcad. I run their YouTube channels, some Creo campaigns, and all Mathcad campaigns and communications.