for windows it is extension=php_pdf.dll and the watermark will disappear if you use the serial in your script:
putenv("serial here"); works for me without problems. for perl pdflib scripts insert
PDF_set_parameter($p, "serial", "serial here"); into the script
to use the fonts insert this line (change path):
putenv("PDFLIBRESOURCE=C:/Programme/Server/PDFLIB_binary/fonts/pdflib.upr");
and in the *.upr file change the path to the fonts directory