"Please print out this form, fill it in, and send back a scan."
Even worse, "Please print out this 20-page contract, sign the last page, scan all 20 pages back in, and email it to us".
So I try to add a scanned signature to the original PDF. Not allowed.
Maybe I can just print the final page, scan it and replace it in the original document. Not possible.
Libre Office can edit PDFs, but the result never looks quite like the original document.
The only solution seems to be to print the thing to 20 single-page image files, edit the final one to add a signature, then assemble them all into a new PDF. But life's not long enough, so print'n'scan it is.