Here's a brief tutorial for removing watermarks.
1. Download and install
https://www.pdfgear.com/pdf-editor-reader
2. Click "Open File" on the left and select the PDF.
3. Click "Edit" on the top.
4. Click "Edit Object" on the top.
5. Press Ctrl+F and type in a portion of the watermark text.
6. Click on the < left or > right button to move between search results.
7. Right click on the watermark on each page and click "Delete"
8. Click the "Save As" icon on the top left.