[pdfrx_engine] add text on top of an existing PdfPage

[MarcVanDaele90]

I want to add a text (~watermark) on top of all pages of an existing pdf file.
I looked at pdfrx_engine but I think that, right now, this is not supported, is that correct?
Would it make sense to add this to pdfrx_engine or is this outside your scope?

[RaadShariat]

PDFRX only renders the PDF files and is not a tool for editing file content (watermarks are part of the PDF content, not extra overlays added by renderers). Wait for the owner's response, but I'm pretty sure that does not fall within the scope of this package.

[espresso3389]

Currently, pdfrx supports Inserting Image as page.

BTW, PR #599 is very similar to your request but it inserts selectable text and not suitable for your use case anyway.