How Long Does PDF Password Recovery Take? Complete Timeline Guide

The four variables that determine recovery time

Variable 1 — Encryption mode: PDF 40-bit RC4 (mode 10400) is always fast regardless of password because the attack is a key-space search (2^40 keys). PDF 128-bit RC4 (mode 10500) runs at ~9.8M passwords/second. PDF AES-128 (mode 10600) runs at ~75K passwords/second. PDF AES-256 (mode 10700) runs at ~28-38K passwords/second.

Variable 2 — Password length and character set: the candidate space is charset_size^length. A 6-character lowercase password (26^6 = 308M candidates) tests in minutes on any GPU. A 10-character full-ASCII password (95^10 = 59.9 quintillion) takes centuries even on large clusters.

Variable 3 — Pattern predictability: most forgotten PDF passwords are human-chosen, not random. Dictionary+rule attacks find 60-85% of human-chosen passwords within hours by testing common patterns first. Brute-force timelines only apply to truly random passwords, which are rare in practice.

Variable 4 — GPU cluster size: a single RTX 5090 is the baseline. Professional services use 8-32 GPUs, dividing timeline by the number of GPUs adjusted for ~94% scaling efficiency per additional GPU.

Mode 10400 (40-bit RC4) — guaranteed fast

Mode 10400 is unique: the attack is a key-space search, not a password search. The encryption key is exactly 40 bits, and every possible key can be tested exhaustively. Password length, complexity, and character set are completely irrelevant.

Timeline on a single RTX 5090: 60-90 minutes for full key-space exhaustion. This is a mathematical guarantee — every one of the ~1.1 trillion possible 40-bit keys is tested. The password is always found.

Multi-GPU scaling for mode 10400: 4 GPUs = 15-23 minutes. 8 GPUs = 8-12 minutes. 16 GPUs = 4-6 minutes. 32 GPUs = 2-3 minutes.

CPU-only timeline: approximately 4-8 hours on a modern 16-core CPU at ~50M keys/second. Mode 10400 is the only mode where CPU recovery is practical.

Mode 10500 (128-bit RC4) — fast GPU throughput

Mode 10500 (128-bit RC4) runs at approximately 9,800,000 passwords per second on a single RTX 5090. This is the fastest password-search mode because RC4's key setup is computationally cheap.

Dictionary+rule attack (10M wordlist, 50 rules = 500M candidates): 500M / 9.8M = 51 seconds on single GPU. 8 GPUs = 7 seconds. This is the most likely successful attack for human-chosen passwords.

Brute-force mask attack timelines for mode 10500 on single GPU: 6-char lowercase (308M candidates) = 31 seconds. 8-char lowercase (208B) = 5.9 hours. 8-char alphanumeric (2.82T) = 3.3 days. 10-char lowercase (141T) = 167 days.

Mode 10500 PDFs date from the 2001-2010 era. Passwords from this period were typically shorter and simpler than modern passwords. The majority of mode 10500 recoveries succeed within minutes, not hours.

Mode 10600 (AES-128) — moderate GPU throughput

Mode 10600 (AES-128 CBC) runs at approximately 75,000 passwords per second on a single RTX 5090. The AES cipher requires more computational work per candidate than RC4, reducing throughput by ~130x compared to mode 10500.

Dictionary+rule attack (500M candidates): 500M / 75K = 1.85 hours on single GPU. 8 GPUs = 14 minutes. Most human-chosen passwords from 2010-2018 fall to dictionary attacks within this window.

Brute-force mask attack timelines for mode 10600 on single GPU: 6-char lowercase (308M) = 68 minutes. 7-char lowercase (8B) = 30 hours. 8-char lowercase (208B) = 32 days. 8-char alphanumeric (2.82T) = 435 days.

Eight-GPU cluster timelines for mode 10600: 8-char lowercase = 4.3 days. 8-char alphanumeric = 58 days. 10-char lowercase = 7.9 years. The practical boundary for mode 10600 recovery on a professional cluster is approximately 9-10 character passwords with moderate complexity.

Mode 10700 (AES-256) — slowest per-candidate rate

Mode 10700 (AES-256 with SHA-256 KDF) runs at approximately 38,000 passwords per second on a single RTX 5090 (50-round KDF) or 28,000 H/s (100-round KDF for PDF 2.0). This is the slowest PDF mode due to the computationally expensive key-derivation function.

Dictionary+rule attack (500M candidates): 500M / 38K = 3.7 hours on single GPU. 8 GPUs = 29 minutes. 32 GPUs = 8 minutes. The dictionary phase is always fast because the candidate count is bounded by the wordlist size, not by brute-force combinatorics.

Brute-force mask attack timelines for mode 10700 (38K H/s) on single GPU: 6-char lowercase = 2.25 hours. 7-char lowercase = 2.4 days. 8-char lowercase = 63 days. 8-char alphanumeric = 2.4 years. 10-char lowercase = 117 years.

Eight-GPU cluster timelines for mode 10700: 8-char lowercase = 8.4 days. 8-char alphanumeric = 117 days. 9-char lowercase = 218 days. 10-char lowercase = 15.5 years. The practical boundary is approximately 8-9 characters with limited charset.

Real-world timelines — how long it actually takes

In practice, most PDF password recovery cases complete much faster than the brute-force worst-case estimates. This is because real-world passwords follow patterns, and pattern-based attacks are tested first.

Fast case (most common): user-chosen password with common patterns. Mode 10500-10700 dictionary+rule attack completes in <1 hour on a professional GPU cluster. 60-70% of all forgotten-PDF cases fall into this category.

Moderate case: password known partially (e.g., 'starts with my dog's name, ends with a year'). Mask attack with known constraints reduces search space by 90-99%. Timeline: 1-7 days on a professional cluster.

Difficult case: password is a moderate-length random string (8-10 characters) with no known pattern. Requires brute-force or combinator attack. Timeline: 30-90 days on a professional multi-GPU cluster. Cost may exceed document value.

Infeasible case: strong random password (12+ characters, full charset) from a password manager. Timeline: centuries. No practical recovery possible. The document must be accepted as permanently lost or replaced from source.

How to get a precise estimate for your PDF

The most reliable way to get a realistic timeline is to run a free analysis with a professional recovery service. The analysis identifies the exact encryption mode (including KDF round count for mode 10700), runs fast dictionary attacks to test common patterns, and provides a timeline estimate based on the actual encryption parameters and your partial password recall.

If you want to estimate yourself: (1) identify the mode with qpdf --show-encryption or the browser-based tool, (2) estimate password characteristics (length range, character types, any known patterns), (3) calculate candidate space (charset_size^length for brute-force, or wordlist_size x rules for dictionary), (4) divide by your GPU throughput (single: 38K H/s for mode 10700, 75K for 10600, 9.8M for 10500; multiply by GPU count x 0.94 scaling).

Remember that dictionary attacks always run first and catch the majority of cases. The brute-force timeline is the worst case and applies only if dictionary and rule attacks fail. Most users never reach the brute-force stage because their password is found in the dictionary phase.

Estimating your PDF recovery timeline

1. 1

   Identify the encryption mode

   Use the browser-based PDF encryption info tool or qpdf --show-encryption to get V/R/Length/CFM values. This sets the per-second password test rate.

2. 2

   Recall what you can about the password

   Length estimate, character types (digits only, lowercase only, mixed), any known substrings or themes. This determines the search space.

3. 3

   Calculate or estimate the candidate space

   charset^length for brute-force. For dictionary: wordlist entries x rule count (typically 10M x 50 = 500M). For mask: constrained positional charset.

4. 4

   Divide by effective GPU speed

   Mode 10700: 38K H/s per GPU x GPU count x 0.94. Mode 10600: 75K H/s per GPU. Mode 10500: 9.8M H/s per GPU. Mode 10400: always 60-90 minutes.

5. 5

   Run the free analysis for the real answer

   The free analysis phase gives you a data-driven timeline using the service's actual GPU cluster, tested against your specific encryption parameters.

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