Short answer: To password protect a PDF on a phone, open arcanizepdf.com/tools/protect in your browser, select the PDF, type a password and tap Protect PDF. The locked copy is created on your device and the original is not uploaded. On Android you can also do it offline with the Arcanize app.
How to lock a PDF in the browser (Android and iPhone)
This works in Chrome, Safari and other mobile browsers, and on a computer.
- Open arcanizepdf.com/tools/protect.
- Tap Select File and choose the PDF.
- Type the password you want to set.
- Tap Protect PDF.
- Tap Download File to save the locked copy.
Anyone who opens the downloaded file will be asked for the password. Keep the original somewhere safe, because a forgotten password cannot be recovered.
How to lock a PDF with the Arcanize Android app
The Arcanize app locks PDFs on your phone without an internet connection.
- Install Arcanize from Google Play.
- Open the app and tap Protect PDF.
- Select the document.
- Enter a password.
- Tap Protect. A password-protected copy is saved to your phone.
Why not use any free online PDF locker?
You are locking the file because it is private. Many online tools need you to upload the unprotected document to their servers before they add the password, which means handing over the exact file you wanted to protect.
Arcanize adds the password inside your browser or in the app, so the unlocked document stays on your device.
How to choose and share the password
| Do | Avoid |
|---|---|
| Use a long password or a short phrase | Your name, date of birth or phone number |
| Send the password by a different channel, such as SMS or a call | Putting the password in the same email as the PDF |
| Keep the original file or save the password in a password manager | Relying on memory for a file you will need later |
A PDF password is only as strong as the password itself. A short or guessable one can be guessed, so length matters more than clever symbols.
Frequently Asked Questions
How do I put a password on a PDF on my phone?
Open the Arcanize Protect PDF tool in your phone's browser, select the PDF, type a password and tap Protect PDF. Then download the locked copy.
Can someone remove the password I added?
Only someone who knows it. Tools that remove a PDF password, including the Arcanize Unlock tool, need the correct password first.
What happens if I forget the password?
It cannot be recovered. Keep the original unprotected file in a safe place, or store the password in a password manager.
Can I lock a PDF inside WhatsApp?
WhatsApp does not have a feature for adding a password to a document. Lock the PDF first, then attach the locked copy.
Is my PDF uploaded when I protect it?
No. The Arcanize web tool adds the password in your browser and the Android app works offline. The document stays on your device.