Payslips, tax documents, contracts, medical reports — some PDFs simply shouldn't be readable by whoever happens to see them in an inbox, a shared drive or a lost laptop. Adding a password is the simplest way to put a lock on a document, and it takes less than a minute.
This guide shows you how, and explains what PDF passwords protect against (and what they don't), so you can choose the right level of security.
The two kinds of PDF password
The PDF standard defines two separate passwords:
- Open password (user password). Required to open and view the document at all. Without it, the content is encrypted and unreadable. This is the one that provides real confidentiality.
- Permissions password (owner password). Controls what someone can do after opening the file, such as printing, copying text or editing.
Permission restrictions are honoured by compliant PDF readers like Adobe Acrobat, browser viewers and macOS Preview, but they are advisory: software that ignores the rules can bypass them. If you need to keep content private, rely on the open password, not on permissions.
How to password protect a PDF
With Password Protect PDF:
- Upload your PDF by dragging it onto the page.
- Enter a password and type it again to confirm.
- Choose permissions — allow or block printing, copying text and modifying the document.
- Protect and download. Open the new file to confirm it asks for the password.
Encryption happens entirely in your browser, so the unprotected document is never uploaded anywhere. That's exactly what you want when the reason you are encrypting is that the file is sensitive.
In this tool, the password you choose is used both to open the file and as the permissions password. Anyone you give the password to can therefore view the document and change its permissions — so share it only with people you'd trust with an unrestricted copy.
Choosing a strong password
PDF encryption is only as strong as the password. A short or common password can be guessed by automated tools very quickly, regardless of the encryption algorithm.
- Use at least 12 characters. Longer is better.
- Consider a passphrase — four or five random words such as
harbour-violet-tunnel-ninetyare both strong and easy to type. - Don't reuse a password from your email or bank.
- Avoid obvious personal information — birthdays, names, phone numbers.
- Store it in a password manager. There is no "forgot password" for a PDF. Lose it and the content is gone.
Understanding encryption strength
PDFs have supported several encryption methods over the years:
| Method | Introduced | Notes |
|---|---|---|
| RC4 40-bit | Early PDF versions | Obsolete; easily broken |
| RC4 128-bit | PDF 1.4 | Widely compatible; considered legacy today |
| AES-128 | PDF 1.6 | Stronger, modern cipher |
| AES-256 | PDF 1.7 extension / PDF 2.0 | Current recommended standard |
Our tool uses RC4 128-bit encryption, which opens in virtually every PDF reader and keeps out casual and accidental access — the right fit for everyday documents like payslips or invoices you're emailing to a known recipient.
For highly sensitive or high-value documents, such as legal evidence, corporate secrets or anything that might face a determined attacker, use AES-256. It's available in Adobe Acrobat (Protect → Encrypt with password), in LibreOffice (File → Export as PDF → Security, using a recent version), and in command-line tools such as qpdf. Whatever you choose, a long, random password remains the most important factor.
How to share a protected PDF safely
Encryption is pointless if the password travels alongside the file.
- Send the password through a different channel — email the PDF, then text or phone the password.
- Agree on a password in advance with people you exchange documents with regularly.
- Never put the password in the email subject or body.
- Watermark sensitive copies (for example, "Prepared for J. Smith — Confidential") with Add Watermark, so a leaked copy can be traced back.
Removing a password you know
If you have the password and want an unlocked copy — for example, to merge the document with others or to stop typing the password every time — use Remove PDF Password. For a file that asks for a password when opened, you need to enter that password: the tool decrypts the file with it and returns an unprotected copy. It doesn't crack or guess passwords. (PDFs that open freely but restrict printing or copying can be unlocked without one.) This tool runs on our server, and the file is deleted immediately after processing.
Please only remove protection from documents you own or are authorised to access.
When a password isn't the right tool
- Sharing with many people? A shared link with access control (Google Drive, OneDrive, Dropbox) lets you revoke access later, which a PDF password can't.
- Need to prove a document hasn't changed? Use a digital signature rather than a password.
- Need to hide part of a document? Use proper redaction, which permanently removes the text, rather than drawing boxes over it.
Frequently asked questions
Can I password protect a PDF on my phone?
Yes. The tool works in mobile browsers on iPhone and Android — upload the file from your Files app, set a password, and save the result.
Does a password make the PDF bigger?
Barely. Encryption adds a negligible amount of data. If the file is too large to email, compress it before adding the password — see how to compress a PDF for email.
Can I add a password to a PDF that already has one?
Remove the existing protection first (you'll need the current password), then apply the new one.
Is my file uploaded when I add a password?
No. Password protection runs locally in your browser. Read more about which tools run locally in our guide to whether online file converters are safe.
Summary
Use an open password for anything confidential, make it long and unique, send it separately from the file, and keep a copy in your password manager. For everyday documents, RC4 128-bit protection is quick and universally compatible. For high-stakes material, step up to AES-256.