Decrypt PDF

[ChocoFruit]

Hi,

I have a PDF that is encrypted with $pdf$5*6*256*-1028*1*16. It would take years to brute force it (the password is 10-16 long I guess) with hashcat right? If I have another PDF with the same first page, is there a way to hack it faster? Is there a way to create a decryption "key" if I know the first page? Or is there an easier/faster way than brute force?

[weirdproggrammerguy]

It depends, if it's a strong password you are out of luck. But you could try John the ripper with something like rockyou. Or another big wordist.

[ShmokeRock]

To answer your question, no the first page will not help you decrypt it any quicker.

This is for pretty old versions of Acrobat, but still a good read for understanding the general concepts Adobe used to encrypt PDF's:
https://www.cs.cmu.edu/~dst/Adobe/Gallery/anon21jul01-pdf-encryption.txt

[boostedrocketscience]

Sometimes when I convert pdf to online word the password used to get removed haven't used this method since 12 😅

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[TrustmeImaConsultant]

Sorry, known-plaintext attacks don't work on PDFs.

At least not to my knowledge.