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I have an encrypted PDF. I have the password for it. 8 alphanumeric characters. But I think when you open it, it makes a connection to a DRM server to check if the content has expired, which it has.

I don't know what type of encryption is used.

I tried the tool pdfcrack which said the type was not supported. I tried pdfcrack.com which said it's a third party encryption.

I find it hard to believe that a university is employing custom encryption schemes. So how do I use a list of known encryption schemes to bruteforce the file until I get a valid PDF out?

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  • So when you decrypt, it opens? Or you decrypt and then open the file? If the second, have you run the pdf through a hex editor?
    – moonbutt74
    Dec 29, 2015 at 2:35
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    If the DRM says the content is expired, then you are legally not entitled to read it anymore. Trying to bypass this limitation would be violating laws, so you will have a hard time to get help with it (Jail, anyone?). I recommend you focus on verifying what really is the problem, and maybe it is not DRM.
    – Aganju
    Dec 29, 2015 at 2:37
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    @Anganju, You presume legal context which OP has not provided. OP may very well be entitled to break the DRM employed.
    – ebpa
    Dec 29, 2015 at 4:01
  • The owner/author apparently went to considerable lengths to create and enforce a limitation on the content. You may be entitled to access it, but the way to do that is not to hack the encryption. The owner/author should be more than happy to provide you the means of access.
    – fixer1234
    Dec 29, 2015 at 6:47
  • Unless the owner/author has been swallowed by a whale and is dead. xD
    – moonbutt74
    Dec 29, 2015 at 7:07

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The PDF standard includes 40/128 bit ARC4 and 128/256 bit AES. Unless the PDF was created a very long time ago or by someone very stupid, it is not using 40-bit ARC4 and you are not going to be able to brute-force the encryption.

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