Protect PDF

What it does

Adding a password to a PDF protects it from casual access — anyone who needs to open the file must enter the password first. The PDF format supports two password types: a “user password” (also called open password) that gates opening the file at all, and an “owner password” (also called permissions password) that gates restricted operations like printing, copying, or editing while still allowing the file to open. This tool sets the user password — the most common request, since it’s what people mean when they say “password-protect this PDF.”

Under the hood, PDF password protection uses AES encryption (AES-128 since PDF 1.6 / 2003, AES-256 since PDF 1.7 ext 8 / 2008). Modern PDF readers — Adobe Reader, Apple Preview, Foxit, Chrome’s built-in PDF viewer, the Office PDF importer — all support AES-128 and AES-256. The encryption is real: without the password, the file content is mathematically inaccessible. (RC4 40-bit and 128-bit are older standards still widely supported but considered weak — modern tools including this one default to AES-128 or AES-256 instead.)

What this tool does NOT do: redact content (use the redaction tool for that), watermark (use the watermark tool), restrict printing or copying without restricting open (that requires owner-password mode), or recover a lost password (impossible — proper encryption means the only path is brute force, which can take centuries for a strong password). All processing happens in your browser via pdf-lib + WebCrypto, so the file never leaves your device. For sensitive documents (legal, financial, medical) this is essential — uploading to a SaaS PDF service exposes the document content to their servers.

How to use it

1. Drop your PDF or browse to select.
2. Choose a strong password (12+ chars, mix of letters/digits/symbols).
3. Optionally re-enter for confirmation.
4. Click Protect — the tool encrypts and offers the protected PDF for download.
5. Test the protected file in Adobe Reader or your target viewer to confirm it prompts for the password.

When to use this tool

• Sending a confidential document via email — even if forwarded, only password-holders can open it.
• Uploading a sensitive PDF to a cloud share (Dropbox, Drive) where you don’t fully trust the security.
• Compliance with policies that require encryption-at-rest for documents with PHI/PII.
• Before sharing tax returns, contracts, medical records, or financial statements with anyone.

When not to use it

• If you need to share with people who can’t reliably enter passwords (elderly relatives, mass distribution, public archives).
• When the destination platform strips PDF passwords on upload (some web forms, some cloud workflows).
• For redaction needs — passwords gate opening; they don’t hide specific text within an opened document. Use redaction tool instead.
• Printing-restricted distribution — that needs owner-password mode (this tool sets user password).

Common use cases

• Verifying a number or output before passing it on
• Quick use during a typical workday
• Pre-decision sanity-check on inputs and outputs
• Educational use — demonstrating the underlying concept