Surprisingly, there is no easy way (at least from what I found) to add some watermark to pdf in batch. (Before)
It's still a WIP, but it's (somewhat) usable now.
This simple scripts add different kinds of text watermarks to a pdf.
Especially, add different watermark (for example, many emails) to the same files.
Please modify the pdf_watermark.py file to suit your need.
you can modify the email_watermark function to change the watermark style for each page. (This maybe change in the future)
For batch watermarks, change the emails.txt file to your own.
In theory, it is possible to add many things as long as it follows the same framework
I will try to add some easy to use functions (hopefully)
Anyway, this is only a toy project for some one-time need.