encryption - Is it true that strongly-password-protected PDF can be cracked?

I want to protect my PDF with a strong password.

But I heard that it can be cracked.

Is it true that strongly-password-protected PDF can be cracked?

Edit: This is my real scenario. I want to sell my ebooks on the web. Recently there are many sites that shares ebooks. I don't want it to happen so I need a password-protected scheme applied to my ebooks. I hope buyers cannot remove and modify the contents; the integrity must be protected.

Answer

Yes, that is true. If that is very important to you, I cannot think of a format that will protect you. There are dozens of tools out there that can break, or remove passwords from PDFs.

It is worth noting, that often passwords can be removed, so it does not matter if it can be broken in the literal sense. Thankfully, they will keep out all but the most determined.

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