Question watermarks for pdf-files?

I have the option of entering watermarks for images.
But I would also like to have this option for pdf-files. Is it possible? If so, how?

Short answer: no.

Long answer: the pdf's come out of the report generator. As I understand it, this is the oldest part of webtrees source code, and rather difficult to maintain or adjust.

If you want to have a go at changing some PHP code, your best bet is to look into the revamped code for reports:
github.com/fisharebest/webtrees/pull/4945
No idea whether it actually is possible in the pdf engine webtrees uses, but such a watermark is like a header or footer, but diagonally placed in large font, light grey coloured, placed behind the actual text.

I had feared this answer too.
Thanks for the explanations.

It might be possible. I found this code:

github.com/Onelinerhub/onelinerhub/blob/...ing-php-and-tcpdf.md

This is fine. But what if the watermark should not be visible when e.g. a user is logged in?