Watermark greyed out?

I’ve read a few posts about watermarking, and read the manual too - but the the option is greyed out on my GUI

Does anyone know how to get around this?

I am just trying to export a bog standard pdf - single part

Watermarking only seems to work when exporting in color, not mono.

Yes, you can’t have a transparent object in a single-colour mode.

Thanks - I never thought to try. I’ll have a go next time.

Last night I spent half an hour looking up YT vids on how to use automator to create the watermark on the pdf!