How to password protect a PDF for free
Drop the PDF onto the box above, type a password (twice for confirmation), and click Protect PDF with password. The encrypted PDF downloads a few seconds later. Open it in Adobe Acrobat Reader, Preview on macOS, or any browser's built-in PDF viewer — each will prompt for the password before showing the content.
Every step happens inside your browser. Your PDF is never uploaded, your password is never transmitted, and nothing is stored on our servers. You can verify by opening DevTools → Network tab while protecting — no upload requests appear.
How do I password protect a PDF without Adobe Acrobat?
Adobe Acrobat's password-protection feature is behind a paid Acrobat Pro subscription (~$20/month). You do not need it. This tool uses the same PDF encryption standard (AES-256 defined in ISO 32000-2) via the open-source @cantoo/pdf-lib library, running entirely in your browser. The output PDF is indistinguishable from one Acrobat produced — same cipher, same standard, same compatibility.
Adobe Reader (the free viewer) does not add passwords — only opens password-protected PDFs. So if you were looking for a way to password protect a PDF document with Adobe Reader, the answer is you cannot; use this tool instead.
AES-256 encryption — what it actually means
AES-256 (Advanced Encryption Standard with a 256-bit key) is the strongest cipher in the PDF specification. It's the same algorithm the US government uses for TOP SECRET classified documents, and the same standard used by Signal, WhatsApp, TLS 1.3 and most modern secure systems. Brute-forcing a 256-bit key would take longer than the age of the universe with all current computing power combined.
The catch: the encryption is only as strong as the password. A 6-character password can be brute-forced in seconds regardless of cipher. Rules of thumb: 12+ characters minimum, mixed case, digits and symbols, and never a real word or common substitution (P@ssw0rd is not strong). Use a password manager — 1Password, Bitwarden, Apple Keychain, Google Passwords — to generate and store passwords.
When should you password-protect a PDF?
- Contracts, NDAs and legal documents sent by email — email is not encrypted end-to-end, so anyone reading server logs or intercepting the message can see the attachment. A password-protected PDF stays confidential even if the email is intercepted.
- Bank statements, tax returns, medical records — same reason. Send the PDF; text the password to the recipient separately (a different channel).
- Salary slips and HR documents shared inside a company's file server — protects against a colleague who stumbles into the wrong folder.
- Client deliverables where you want to prevent casual copying or modification (we set copying and modifying permissions to disabled by default).
- Personal ID copies (passport, driver's license, Aadhaar, PAN) that you sometimes need to email or upload — a password stops opportunistic identity theft.
How to remove the password later
If you set a password today and later want to remove it (maybe you're sending the PDF to someone you'd rather not text the password to), use our PDF Unlock tool. Drop the protected PDF, enter the password, and download an unlocked copy. Same browser-only process, no upload.
What is inside a password-protected PDF?
A password-protected PDF is a normal PDF file with an added encryption layer over its content streams. When a viewer opens it, the file header reveals that the content is encrypted; the viewer prompts for the password, derives an encryption key from the password using PBKDF2 or similar key derivation, and then decrypts the content on the fly for display. The password itself is never stored in the file — only a verification hash. This is why forgotten passwords cannot be recovered from the PDF.
How to password protect a PDF on iPhone or Android
Open this page in Safari on iPhone, Chrome on Android, or any modern mobile browser. Tap the drop zone and pick the PDF from Files, Downloads, iCloud Drive, Google Drive, or wherever you keep it. Type your password twice and tap Protect. The encrypted PDF downloads to your device. No app install needed. Works identically on tablets — iPad, Android tablets, Chromebook.
Privacy — nothing uploaded, ever
Both the PDF file and the password are processed in your browser using JavaScript and WebAssembly. Nothing about the document, the password, or even the file name reaches our servers or any third party. This is the whole point of a client-side tool: your confidential PDF (contract, medical record, tax return) never becomes someone else's problem to protect. If we're hacked tomorrow, your document is still safe because we don't have it.