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In the replies to how to remove the password from a pdf file, some solutions (e.g. by ghostscript) require no password, while some (e.g. by pdftk) do.

Is knowing the password necessary for removing it from a pdf file? If not, then

  • why do some solutions (e.g. by pdftk) require the password? What are their advantages over those solutions that don't require the password?

  • what is the purpose of setting up a password for a pdf file? Does it try to prevent those without the password from reading and writing the pdf file? Does it prevent those without the password from printing/copying the pdf file to another pdf file without any password, an indirect way to read the original pdf file, and the idea of the pdftk and ghostscript solutions?

Tim
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    I don't think there are solutions that don't require the password. The ghostscript ones will presumably prompt for the password, you just don't pass it on the command line. This is mentioned in the comments. – terdon Aug 10 '23 at 11:38
  • I remember gs didn't ask anything when I tried it on a password-protected pdf file – Tim Aug 10 '23 at 12:25
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    But was it password protected for editing or for viewing? If it was for viewing and you could remove the password without knowing the password, then protection would be 100% pointless. Which might be the case, it just seems weird. – terdon Aug 10 '23 at 12:46

2 Answers2

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One may try to use programs that try to guess the password of the PDF file via bruteforce, e.g. pdfcrack:

sudo apt install pdfcrack

If the password is just for editing the PDF, one can view the PDF file in some PDF viewer e.g. with Chrome's built-in PDF viewer, and print it as a PDF file. The new PDF file won't have any password.

Franck Dernoncourt
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If the PDF file has a password on it, you will need to know the password to remove it.

Mr. T
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