Watermark contrib

Merge request template

Contrib script to watermark a page on a given pdf file. executing:

watermark_document_page.py Lorem_ipsum.pdf

changes this:

to this:

Options:

• [-t, --text TEXT]: use a string other than "DIGITAL COPY".
• [--overwrite]: don't write to a new file in CWD, instead overwrite the provided file.
• [-p, --page PAGE]: the page to watermark (0-based), default is 0.

If successful, prints the name of the saved file.

Changelog entry

• This change does not need a changelog entry.

Anything else

Not a script specifically related to Plom, but maybe has some utility.