Encrypt PDF

Purpose

Set passwords on a PDF — both an open password (required to view) and an owner password (controls permissions: print, copy, edit). Algorithm options: AES-256 (PDF 2.0, strongest), AES-128 (Acrobat 9+ compatible), or RC4-40 (weakest, only for legacy Acrobat 4). Runs locally via qpdf-wasm; no upload, no watermark, free. Use it to protect contracts, financial reports, customer data against unauthorized access.

Steps

1. Drag or pick a PDF
2. First use downloads the ~2MB qpdf engine (one-time)
3. Decide if you want an open password (required to view the PDF)
4. Enter the open password and confirm
5. (Optional) Set an owner password to control permissions
6. If set, configure permissions: allow printing, copying text, modifying annotations, filling forms
7. Pick the cipher: AES-256 (recommended) / AES-128 / RC4-40 (deprecated)
8. Click "Process"
9. Download the encrypted PDF, suffix "-encrypted"

FAQ

Is AES-256 really unbreakable?

AES-256 is considered the strongest commercial encryption — brute-forcing it would require 2^256 attempts (effectively universe-lifetime durations). The real weak link is password strength: weak passwords (e.g., 123456) fall to dictionary attacks in seconds; strong passwords (12+ chars mixing case/digits/symbols) paired with AES-256 are practically uncrackable.

Will the file be uploaded for encryption?

No. qpdf-wasm is a WebAssembly-compiled crypto engine that runs in your browser — the PDF and password never leave your device. Inspect DevTools yourself: zero outbound requests.

Should I pick AES-128 or AES-256?

Trade-off: compatibility vs strength. AES-128 works with Acrobat 9+ (2008-and-later) and is strong enough for most use cases. AES-256 is PDF 2.0 (2017) standard, needing Acrobat XI/Reader DC or newer to open. If your recipient runs older software, AES-256 may fail to open.

Can I recover a forgotten password?

No tool worth trusting can — that's the design goal of AES. Use a password manager (Bitwarden, 1Password) to store important PDF passwords.

Does encryption inflate file size?

Hardly. Encryption adds only a few hundred bytes of metadata; compression ratio is virtually unchanged.

Use cases

• Encrypt contracts before email to prevent unauthorized inspection in transit
• Encrypt employee payroll PDFs before emailing
• Encrypt customer-data archives for protected storage
• Encrypt financial reports before distribution to the board
• Encrypt bid submissions for tender deadline delivery

Tip

Set both an open password (gates viewing) and an owner password (refines permissions like print/copy). Strong passwords are at least 12 mixed characters — weak passwords negate the encryption.