qpdf - PDF encryption and decryption

Qpdf is a command-line PDF encryption (password protect) and decryption (remove password) tool which is the next generation of PdfCrypt now retired.

Supports these five kinds of encryption/decryption:

• 40-bit encryption (method 40bit) in Acrobat 3 (PDF 1.1) and above
• 128-bit encryption (method 128bit) in Acrobat 5 (PDF 1.4) and above
• 128-bit AES encryption (method AES) in Acrobat 7 (PDF 1.6) and above
• 256-bit AES encryption (method AES256) in Acrobat 9 (PDF 1.7) – this is deprecated – do not use for new documents
• 256-bit AES encryption (method AES256ISO) in PDF 2.0

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