If you've sent a crew member a PDF with a watermarked file, they will not be able to add notes on the PDF. This is a security measure set to prevent someone from removing the watermark after they download it.
The password that's added to the document is set by Adobe and the password is hidden in a mountain castle guarded by trolls. That's not true, but what is true is that SetKeeper can't control it.
However, there are some workarounds:
For Mac users: they can view the PDF in "Preview" and save a copy of the file from there. They should be able to add notes to their saved copy.
For PC users: You can also try the steps in this article from Adobe (as long as Adobe is the program they're using to open PDFs).
We've gotten this feedback before - that people want to be able to take notes on watermarked PDFs - and I hope we can make it a feature in future software releases!