Robust PDF editing on the fly

Hello!, Longtime member, rare poster here. I am browsing around right now regarding the subject line, and have looked at the HTML_toPDF project http://www.rustyparts.com/pdf.php that also includes a PDFEncryptor system in it.. but I thought I'd post to the list to see if anyone has any recommendations or comments. I'm particularly looking at editing some of the more advanced security features of PDF (if possible) on-the-fly.. things such as limiting printing, encryption etc.. I am building some basic epub sale/distrobution/DRM features for a client. TIA for any comments! Donovan -- D Brooke