You can remove the Adobe watermark from the tryout project file only after you purchase the product. You can not remove the Adobe watermark from an export from the tryout product even after purchase.
To remove the Adobe watermark from the tryout project file, you open it in the purchased version and then
Timeline Menu/Delete Rendered Files...render Timeline content
That is the classical way. Some of us have found that just opening the project file in the purchased project removes the Adobe watermark automatically. You will need to determine which one works for you.
Any questions, please do not hesitate to ask.