Best way to REALLY secure a PDF

We need to send our customer a secured PDF's which he'll not be able to edit at all.
I came across this article which shows how to crack those so-called protected files.

Please advice on how to really secure those documents.

Thanks in advance
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Rich RumbleConnect With a Mentor Security SamuraiCommented:
Well said McKnife, you can OCR a pdf from sceenshots, OCR software comes with every 3-in-one printer out there for free, you can also find many OCR software free as well. If you can open the PDF you can get it's contents out. But if you want tough encryption that takes forever to break, use a long password and a modern PDF maker.
The AES256 is the hardest method available, and the slowest. The 40-bit RC4 is the weakest and is what you get when you save a word doc as a pdf in 2007-2013 when you add encryption... so BUY AdobePDF maker and get the best encryption.
You can even try to buy the more fancy FileOpen software, but it too has been defeated in the past, but it offers the overall best security features I've seen.
Still if it can be opened, it can be copied one way or another, screen shots being the easiest method.
Dave BaldwinConnect With a Mentor Fixer of ProblemsCommented:
The only way I know that is more secure is to create the PDF with images instead of text.  Even then, if you put black text on a white background I could probably change some things.

What is being done with this PDF that makes it necessary to be 'secure'?
McKnifeConnect With a Mentor Commented:
If I read REALLY, it seems to me you're hoping for some solution to REALLY cover ALL possible attacks. There ain't. Whatever you do to the document, it still has to be readable and that will enable any reader to somehow copy the screen contents and turn them back into an electronically readable AND fully modifiable form. In between there's not much effort.
IT_Group1Author Commented:
Thank you guys
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