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· pdfcrack · pdf · password-recovery · password-cracking · hashcat · john-the-ripper · linux · macos · security

pdfcrack — recover lost PDF passwords on Linux and macOS (2026)

pdfcrack is a small, single-threaded CPU tool for recovering lost PDF user and owner passwords. Fine for 40-bit RC4 and small dictionary attacks; for 128/256-bit AES PDFs, migrate to pdf2john + hashcat on a GPU.

TL;DR — pdfcrack is a command-line tool that recovers the user password or owner password of an encrypted PDF by brute-force or dictionary attack. It’s small, written in C, runs on Linux/macOS/WSL, and handles every encryption profile PDF has shipped — 40-bit RC4, 128-bit RC4, 128-bit AES, 256-bit AES (PDF 1.7 + 2.0). It is single-threaded and CPU-only, so it is fast on the weak old RC4-40 encryption but increasingly slow as PDFs get modern. Install with apt install pdfcrack (Debian/Ubuntu), brew install pdfcrack (macOS), or build from source. When pdfcrack is too slow, switch to pdf2john + hashcat on a GPU.

This walkthrough assumes you have authorisation to recover the password on the PDF — your own document, a client’s, or a legally-acquired file. Don’t attack PDFs you don’t own.

User password vs owner password

PDF has two passwords:

  • User password — required to open and read the document.
  • Owner password — required to remove restrictions (print, copy, modify) on a document that opens without a user password.

Many “protected” PDFs are only owner-password-restricted: they open fine, but printing and copying are disabled by the reader. Those are trivial to unlock — qpdf --decrypt or any of the pdftk-style tools strip owner-only restrictions without needing to guess anything. pdfcrack is for the harder case: a user-password-protected PDF you can’t open at all.

Check which you’re dealing with:

$ qpdf --show-encryption document.pdf
R = 6
P = -3904
User password = 
Supplied password is owner password
extract for accessibility: allowed
extract for any purpose: not allowed
print low resolution: allowed
print high resolution: not allowed
modify document assembly: not allowed
modify forms: not allowed
modify annotations: not allowed
modify other: not allowed
stream encryption method: AESv3
string encryption method: AESv3
file encryption method: AESv3
  • R = ... tells you the revision / profile. R=2 = RC4-40, R=3 = RC4-128, R=4 = AES-128, R=5/6 = AES-256.
  • “Supplied password is owner password” + “User password = (empty)” means you can open it and just need to strip restrictions. Use qpdf --decrypt --password='' input.pdf output.pdf and you’re done.

Install

# Debian / Ubuntu / Mint / Kali
sudo apt install pdfcrack

# macOS (Homebrew)
brew install pdfcrack

# Arch / Manjaro
sudo pacman -S pdfcrack

# Fedora / RHEL
sudo dnf install pdfcrack

# From source
wget https://sourceforge.net/projects/pdfcrack/files/latest/download -O pdfcrack.tar.gz
tar xf pdfcrack.tar.gz && cd pdfcrack-*
make
sudo cp pdfcrack /usr/local/bin/

Benchmark

$ pdfcrack -b
Benchmark:	Average Speed (calls / second):
MD5:			1728972.6
MD5_50 (fast):		 97879.3
MD5_50 (slow):		 69167.0

RC4 (40, static):	606555.3
RC4 (40, no check):	598050.0
RC4 (128, no check):	590141.7

Benchmark:	Average Speed (passwords / second):
PDF (40, user):		453510.2
PDF (40, owner):	220250.0
PDF (40, owner, fast):	499995.0

PDF (128, user):	 22000.0
PDF (128, owner):	 10408.7
PDF (128, owner, fast):	 22220.0

Translation:

  • RC4-40 (PDF 1.3, very old) — ~450k passwords/sec. Brute-force of a full 8-character alphanumeric space: ~1 week on one core.
  • RC4-128 / AES-128 — ~22k passwords/sec. Brute-force becomes unrealistic above length 6 with any charset.
  • AES-256 (R=5/6) — even slower; pdfcrack does support it but effectively only for dictionary attacks against small wordlists.

If you need speed beyond this, you want hashcat on a GPU. Numbers at the bottom.

Dictionary attack

pdfcrack -f document.pdf -w /usr/share/wordlists/rockyou.txt
  • -f — target file.
  • -w <file> — wordlist, one candidate per line.
  • Optional -o — attack the owner password only (ignore user password). Default is to try user password first.
  • Optional -u — attack user password only.

If you have context — the password is probably a first name, a year, a project code — assemble a smaller targeted list. Generic lists are a long shot once you’re past the top ten thousand entries.

Brute-force attack

pdfcrack -f document.pdf -c 'abcdefghijklmnopqrstuvwxyz0123456789' -n 4 -m 8
  • -c <charset> — character set to try. Default includes a broad ASCII range.
  • -n <min> — minimum length.
  • -m <max> — maximum length.

Tune -c aggressively. If you know the password is all lowercase, don’t give it uppercase. If you know it has a digit at the end, use a mask attack (hashcat territory, not pdfcrack).

Resume a long run

pdfcrack -f document.pdf -w rockyou.txt -s /tmp/state.sav

-s writes periodic save files; if you kill pdfcrack and restart, pass -l /tmp/state.sav to resume.

When to switch to hashcat

For any modern PDF (R=4, 5, or 6 — i.e. AES-128 or AES-256), pdfcrack’s single-core speed becomes the bottleneck. pdf2john + hashcat gets you two to three orders of magnitude more throughput on a GPU.

Step 1: extract the hash

$ /usr/share/john/pdf2john.pl document.pdf > hash.txt

(On Debian/Ubuntu: apt install john provides pdf2john.pl.)

Step 2: identify the hash mode

$ head -1 hash.txt
document.pdf:$pdf$5*6*256*-1028*1*16*...

Map the first two numbers:

  • $pdf$1*2*... → mode 10400 (PDF 1.1–1.3, RC4-40, user)
  • $pdf$1*2*... with owner salt → mode 10410 / 10420
  • $pdf$2*3*... → mode 10500 (PDF 1.4–1.6, RC4-128 / AES-128)
  • $pdf$5*5*... → mode 10600 (PDF 1.7 r=5, AES-256)
  • $pdf$5*6*... → mode 10700 (PDF 1.7 r=6 / PDF 2.0, AES-256 with PBKDF2)

Step 3: run hashcat

hashcat -m 10700 hash.txt /path/to/wordlist.txt

On a single modern GPU (e.g. RTX 4090):

  • Mode 10400 (RC4-40): ~10 billion H/s — any practical password is recovered instantly.
  • Mode 10500 (RC4-128 / AES-128): ~100 million H/s.
  • Mode 10700 (AES-256, PBKDF2): ~50,000 H/s. This is by design — the PBKDF2 iterations make brute-force expensive.

For mode 10700, your attack strategy matters more than raw speed. Dictionary + rules + mask attacks targeted at likely password patterns are orders of magnitude more productive than exhaustive brute-force.

Common gotchas

“File seems encrypted but I can still open it without a password”

You’re looking at owner-only restrictions. Use qpdf --decrypt input.pdf output.pdf — no cracking needed.

pdfcrack runs but never finds anything

Three likely causes:

  1. Password is longer / more complex than your charset × length covers. Increase -m and/or expand -c, or switch to a dictionary.
  2. Password contains non-ASCII characters. pdfcrack’s charset is ASCII by default; non-ASCII user passwords in old PDFs used varying encodings (PDFDocEncoding, UTF-16). Try pdf2john + hashcat, which handles the encoding properly.
  3. It’s AES-256 (R=6) and you’re being patient. See speed notes above — realistic only with a dictionary.

“Only AES-256 is supported” error or similar

Your pdfcrack build is old. Ubuntu LTS sometimes ships a version that doesn’t fully handle R=6. Build from source or switch to pdf2john + hashcat.

PDF opens but printing/copying is blocked

That’s owner-password-restricted only. qpdf --decrypt without needing a password usually works:

qpdf --decrypt --password='' input.pdf output.pdf

Defensive takeaway

For anything you want to stay encrypted in 2026, use AES-256 with a PDF 2.0 (R=6) password. That’s the profile with PBKDF2 key derivation that makes offline attacks expensive on current hardware.

And, as always, the password’s length matters more than anything else. A 20-character random passphrase is brute-force-intractable against any current GPU. A 6-character “clever substitution” password is a coffee break on an RTX 4090.

FAQ

Is pdfcrack still maintained?

Updated slowly. The codebase handles all currently shipped PDF encryption profiles; it just isn’t where performance work is happening anymore (that’s hashcat).

Does pdfcrack use GPU?

No. CPU-only, single-threaded. For GPU work, use pdf2john + hashcat.

Can pdfcrack recover the document if the creator cleared the user password but kept the owner password?

Yes — use qpdf --decrypt first; if that won’t fully decrypt, pdfcrack -o attacks the owner password.

Does pdfcrack leak my PDF anywhere?

No. It’s local. Anything online-only (“crack my PDF at cloud-service-X.com”) involves uploading the file, which you shouldn’t do for confidential material.

What if I only vaguely remember the password?

Write down what you remember — likely words, likely digits, likely length — and build a targeted wordlist or hashcat mask (-a 3 ?l?l?l?l?l?d?d?d?d). That beats any generic list.

Can I recover text from an AES-256 PDF without the password?

No. AES-256 with PBKDF2 (R=6) is, to the best of public cryptanalysis, not broken. If the password is strong and lost, the contents are lost.

Summary

  • Owner-password-only? qpdf --decrypt, no cracking needed.
  • User-password-protected, old (R=2/3)? pdfcrack with a dictionary works fine.
  • Modern (R=4/5/6)? pdf2john + hashcat on a GPU, targeted attack.
  • Strong 20-character random? Accept the loss.