Password Protect PDF with AES-256 Encryption

1. 00

   What’s great about our PDF password protector

   • Free
   • Super fast
   • No PDF uploads
   • No PDF downloads from the server
   • Your password never leaves your device
   • Works offline
   • No daily limit
   • No ads
   • No watermarks
   • Strong AES-256 encryption
   • 4, 6, 8 or 10-digit PIN, or a custom password
   • Built-in password generator and strength check
   • Optional blocks on printing, copying and editing
   • Live preview of every page
   • Batch protect with ZIP download
   • Every file is test-opened before you download it
2. 01

   Choose your PDFs

   Pick one or more PDFs from your device, or drag them in. They load straight into your browser's memory — they are never sent anywhere.

3. 02

   Set a password

   Choose a 4, 6, 8 or 10-digit PIN, or Custom for a password of your own. Type it twice, or tap Generate for a strong random one. Then save it somewhere safe, because it can’t be recovered if you forget it.

4. 03

   Protect and download

   Click Protect PDF, then Download to save the locked PDF straight to your device. It asks for your password every time it is opened.

5. 04

   Protect many PDFs at once

   Choose several PDFs together, or tap ‘+ Add More’ to add others later. Click Protect PDF once and they are all locked with the same password. Then click Download to save them all together as a ZIP. It’s super fast, simple, and private.

6. 05

   Loved it?

   • If you're on computer, bookmark this page to your browser.
   • If you're on mobile, add it to your home screen for one-tap access and offline use.
     • Android: Visit this page in Google Chrome > tap three-dot icon (⋮) at top > Install and create shortcut. See screenshots for help.
     • iPhone and iPad: Visit this page in Safari > tap menu icon in address bar > Share > Add to Home Screen. See screenshots for help.

How it works

• Choose one or more PDFs, pick a PIN length or Custom, and type your password twice. Or tap Generate to create one for you.
• Click Protect PDF. Every PDF is locked right in your browser with AES-256, using a key that is protected by your password.
• Each result is opened again and checked before you can download it: it must ask for a password, reject a wrong one, open with yours, and keep its pages and text. If any check fails, no file is offered.
• Optionally block printing, copying text or editing. These ask PDF apps to hold back, and the password is what truly keeps people out.
• See All Pages is ticked by default, so every page of each PDF shows as a grid of small thumbnails. Use the two icons beside it to switch to a vertical list of large pages, which opens at 150% zoom on a computer and fits the screen on a phone. Change the zoom with the + and − buttons.
• Untick See All Pages to show each PDF as one small thumbnail with page arrows instead.
• With two or more PDFs added, the Jump to PDF menu above the files shows which PDF you are on and scrolls straight to the one you pick.
• Download one PDF on its own, or all of them together as a ZIP.
• Nothing is uploaded. Once the page has loaded, it keeps working offline.

Frequently asked questions

• Is my PDF uploaded anywhere? No. Protection runs entirely in your browser. Your PDF and your password are never sent to a server, so both stay private.
• How strong is the protection? Your PDF is locked with AES-256, the strongest encryption the PDF standard supports. How hard it is to break then depends on your password: a short PIN can be guessed by a computer far faster than a long custom password.
• What if I forget the password? If you forget the password, it may be extremely hard or impossible to recover it and regain access to your PDF. Nothing is stored or sent anywhere, so no one can reset it for you. Save the password somewhere safe, and keep an unprotected original of the PDF in a safe place too.
• Should I use a PIN or a custom password? A PIN is quick to type but has few combinations: 10,000 for 4 digits and 10 billion for 10 digits. For anything sensitive, choose Custom and use the Generate button or a long mix of letters and numbers.
• Can I protect several PDFs at once? Yes. Add as many PDFs as you like, and they are all locked with the same password. Download them together as a ZIP or one at a time.
• Will the protected PDF open on my phone and in other apps? Yes. It opens in Adobe Acrobat, Chrome, Firefox, Edge, Safari, Preview and most phone PDF readers, which ask for the password first. A few very old PDF readers may not support AES-256.
• What do the extra restrictions do? They ask PDF apps to block printing, copying text or editing. Most apps respect this, but the restrictions are enforced by the app rather than by the encryption, so some apps can ignore them. The password is what truly locks the file.
• Which PDFs are not supported? PDFs that already have a password cannot be processed, so remove the old password first. Digitally signed PDFs can be protected, but rewriting the file invalidates the signature.

What happens to your PDF

• Encryption: every page, image, font and piece of text inside the PDF is encrypted with AES-256 using a random key made fresh for each file. That key is itself locked by your password, using the strengthened method from the latest PDF standard.
• Your password: it is used once, in memory, to lock the file. It is not stored, not logged and not sent anywhere, and it is gone when you close or refresh the page.
• Owner password: a separate random one is created for each file and thrown away. It only matters for the optional restrictions, and nobody, including you, can use it afterwards.
• Your content: pages, text, images, links, bookmarks and forms look exactly the same once the PDF is opened with the password. The file only grows slightly.
• Hidden details: the title, author and other document details are encrypted too, so they can’t be read without the password.
• Still visible: the file name and file size stay readable to anyone who has the file, so give it a neutral name in File Name.
• Safety check: the locked PDF is opened again here to confirm that it asks for a password, rejects a wrong one, opens with yours, and keeps the same pages and text. If anything differs, you don’t get a file.

How to get the most out of it

• Use Custom for anything sensitive. A long mix of letters and numbers, or the Generate button, is far harder to guess than a PIN.
• Save the password first. Put it in a password manager or another safe place before you share the file. If it is lost, the PDF may stay locked for good.
• Keep an unprotected original. This tool never changes your original file, so store it somewhere safe in case the password is lost.
• Send the password separately. Share the PDF by email, and the password by a different route such as a call or message.
• Avoid guessable passwords. Birthdays, names, phone numbers and common words can be tried first by anyone attacking the file.
• Pick PINs with care. A PIN is convenient, but a computer can try every 4, 6 or 8-digit PIN quickly. Use it to keep casual eyes out, not for highly sensitive files.
• Give the file a neutral name. The name stays visible even though the contents are locked.
• Do many at once. Add all your PDFs together and download them as one ZIP. They share one password, so run separate batches if you want different passwords.
• Know the limits. PDFs that already have a password can’t be processed, and digitally signed PDFs lose their signature when rewritten.

How it compares with iLovePDF

• Privacy: iLovePDF uploads your PDF to its servers and deletes it automatically after 2 hours. Here nothing is ever uploaded. Your PDF and its password stay on your device.
• Password options: iLovePDF asks you to type a password twice. This tool does that too, and also offers ready-made 4, 6, 8 and 10-digit PIN options, a password generator and a strength check.
• Limits: this tool needs no account, has no daily limit and adds no watermark. Your device's memory is the only limit.
• Offline: iLovePDF offers a desktop app and mobile apps. This page keeps working offline once it has loaded, and can be installed as an app from your browser.
• Checking the result: this tool re-opens every protected file to confirm that the password works before you download it.
• What iLovePDF has that this doesn't: importing files from Google Drive or Dropbox, desktop and mobile apps, and a large set of other PDF tools such as merge, split and compress. This page does one job only.
• Results: both lock your PDF with a password, so how well it is protected depends mostly on the password you choose.

How it compares with other popular PDF password tools

• Smallpdf: works in the cloud, deletes files after one hour and says it uses 128-bit AES encryption. Here your PDF is never uploaded, and it is locked with AES-256.
• Adobe Acrobat online: its free password tool needs no sign-up to try, while restricting printing, copying or editing needs Acrobat Pro, which has a seven-day free trial. Here those restrictions are free.
• PDF24: its online tool advertises 256-bit AES and adjustable permissions, and is free with advertising. Its online tools upload your file and delete it after one hour, while its free PDF24 Creator app works offline on Windows.
• Sejda: its free online tool covers documents up to 200 pages or 50 MB and 3 tasks per hour, and deletes files after 2 hours. Sejda Desktop keeps files on your computer. Here there is no page, size or hourly limit beyond what your device can handle.
• The main difference: these online tools process your PDF on their servers, so both the file and its password have to be sent first. Here everything happens inside your browser, which matters most for contracts, ID documents and other private files.
• Trade-off: a cloud service does the work on its own servers, so it can handle extremely large PDFs more easily. Here, very large files depend on your device's memory and may be slow on a phone. Many of these sites also offer other tools, while this page only adds passwords.
• Note: these details come from each service's own website as of September 2026 and can change.