Password Protect a PDF
Add AES-256 encryption to a PDF — the file and your password stay in your browser and are never uploaded. Protecting a file needs a free account.
How to password protect a PDF without uploading it
- Pick a PDF — drag it in or browse from your device. It is opened directly in your browser, not uploaded.
- Choose a password — this is what anyone will need to open the document. Type it twice so a slip of the finger doesn’t lock you out of your own file.
- Decide what readers may do — printing, editing and copying text can each be allowed or blocked. Add a separate owner password under Advanced if you want to keep change rights for yourself.
- Download the protected copy — a WebAssembly build of qpdf encrypts it locally with AES-256. Your original file is never modified.
When to password protect a PDF
Anything you would not leave on a printer tray: salary slips and offer letters, bank and card statements, medical reports, signed contracts, ID scans, board papers, exam papers before the exam. A password is also the only practical protection for a document that will travel by email or WhatsApp, where you lose control of who forwards it. Send the password separately — over a call or a different app — so a single intercepted message never carries both.
Stop a PDF being printed, copied or edited
Encryption decides who can open the document; permissions decide what they may do once it is open. Under Advanced you can block printing, block editing, and block text copying and extraction independently — useful for a report you want read but not lifted from, or a price list you would rather was not reprinted. Setting a separate owner password there is what keeps those choices yours: it is the password that lifts the restrictions, so without it a reader keeps only the rights you granted.
Be clear-eyed about the strength of this. Permission flags live inside the encrypted file and mainstream readers — Acrobat, Preview, Chrome, Edge — honour them, but they are a convention rather than a lock, and software that ignores them exists. They state your intent unambiguously and stop casual reuse; the encryption and a long open password are what actually protect the contents. If you later need those restrictions gone from your own file, the Unlock PDF tool removes them.
Private by design
A password tool that uploads your file is a contradiction: the server sees the document and the password in the clear before it encrypts anything. This one never does. The whole encryption engine — qpdf, compiled to WebAssembly — runs inside your browser, so confidential documents stay on your machine, and the tool keeps working if you go offline after the page loads. The background worker holding your password is destroyed the moment the job finishes. Read more in our privacy policy.
Need the reverse? The unlock tool removes a password you already know. You can also sign, watermark or compress a document before you lock it — do the edits first, since a protected file has to be unlocked again to change it.
Frequently asked questions
Can I password protect a PDF without uploading it?
Yes. Encryption runs entirely in your browser using a WebAssembly build of qpdf. The document and the password you type are held in your browser's memory for the few seconds the job takes, then discarded — the worker that handled them is destroyed after every run. Our pages ship a Content-Security-Policy that blocks the page from contacting any other server, so this is enforced by the browser, not just promised.
Why do I need an account for this tool?
Because it changes a document's contents — it writes a new, encrypted copy of your file. Every tool in that group is offered to signed-in members who have accepted our Acceptable Use Policy, so that the undertaking not to misuse them is given by someone identifiable. A free account is enough. It changes nothing about your file: the encryption still happens entirely in your browser, and neither the document nor the password is ever uploaded.
How do I stop a PDF from being printed or copied?
Open Advanced and turn off printing, editing or text copying — each is a separate switch — then set an owner password alongside them, since that is the password which lifts the restrictions. Mainstream readers honour these flags, but they are a convention rather than a lock: use them to state your intent and prevent casual reuse, and rely on the encryption and a long open password for real protection.
How strong is the encryption?
The file is encrypted with AES-256, the strongest scheme the PDF specification defines and the one Acrobat has used since PDF 2.0. The practical strength is your password: a short or common one can be guessed offline no matter how good the cipher is, so use a long passphrase.
What is the difference between the open password and the owner password?
The open (user) password is what someone must type to read the document at all. The owner password lifts the permission restrictions — printing, editing, copying text. If you set only an open password, anyone who can open the file also has full permissions once it is unlocked. Set a separate owner password under Advanced when you want to share reading access while keeping change rights to yourself.
Can the permission restrictions actually stop someone printing or copying?
Not absolutely. Permission flags are part of the encrypted file and mainstream readers such as Acrobat, Preview and Chrome honour them, but they are a convention — software that ignores them exists. Treat permissions as a clear signal of intent; the encryption and your password are what genuinely protect the content.
What if I forget the password?
The file cannot be recovered. We hold no copy of the document or the password, and AES-256 has no backdoor. Store the password in a password manager before you delete the original.
Will the protected PDF open everywhere?
Yes — AES-256 encryption is supported by Acrobat, Apple Preview, Chrome, Firefox, Edge and every current mobile PDF reader. Very old software (roughly pre-2017 readers stuck on PDF 1.6) may not open it.
Can I protect a PDF that already has a password?
Not directly — remove the existing password first with our Unlock PDF tool, then protect the result with the new one.
Is there a file size limit?
About 50 MB. The encryption engine runs inside the browser's WebAssembly memory, which is capped (more tightly on phones), and a larger file would fail unpredictably rather than slowly. If yours is bigger, run it through our PDF Compressor first.
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