Here's a little perl script to remove the prince watermark note from a pdf:
perl -p -e '!$x && s:/Annots \[[0-9]+ 0 R [0-9]+ 0 R ?([^\]]+)\]:/Annots [\1]: && ($x=1)' input.pdf > output.pdf
Update:
So, unfortunately the simple perl hack will “damage” the pdf. It seems that most viewers will ignore this, but I was alerted that a popular ipad reader “GoodReader” produces an ominous “This file is damaged” warning (though it then renders OK).
I couldn’t quite reverse engineer why, but here’s a temporary albeit heavy-handed fix. After running the perl script, also repair the pdf with ghostscript:
gs -o output.pdf -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress input.pdf
Note that output.pdf cannot be the same as input.pdf or it quietly creates an empty pdf instead.
Update:
Even better you can directly remove the specific Annotation from prince:
perl -i -p -e 's:/(Rect \[572\.0000 716\.0000 597\.0000 741\.0000\]|Contents \(This document was created with Prince, a great way of getting web content onto paper.\))::' input-and-output.pdf
Update:
Or even even better better:
perl -i -pe 'BEGIN{undef $/;} s:/Rect.*?Contents \(This document was created with Prince, a great way of getting web content onto paper.\)::smg' input-and-output.pdf