Skip to content
Scansy

How to password-protect a PDF on Android

Add a password to a PDF on your Android phone before you email it or store it somewhere shared, without uploading it to a website to do it.

In short

  • A PDF password encrypts the file, so it stays protected wherever it goes.
  • Use a long passphrase and keep it in a password manager.
  • Send the password through a different channel from the file.
  • Keep an unlocked original: forgotten passwords can’t be reset.

When a password is worth it

Most PDFs don’t need a password. But some documents travel further than you’d like: an email gets forwarded, a shared folder is shared again, a phone is lost. For those, a password on the file itself means the content stays protected wherever the file ends up.

Good candidates are:

  • scans of passports, ID cards and driving licences;
  • bank statements, payslips and tax documents;
  • medical letters and test results;
  • contracts and anything with a signature on it;
  • documents you’re sending by email or storing in a shared cloud folder.

How PDF password protection works

A PDF can carry an “open” password (sometimes called a user password). When it’s set, the contents of the file are encrypted, and any PDF reader will ask for the password before showing a single page. Without it, the file is unreadable data.

This is different from simply hiding a file in a locked folder or app. The protection is inside the PDF, so it still applies after you email the file, upload it or copy it to another device. The flip side: if you forget the password, there is no reset link. Whoever locked the file needs to remember it.

Step by step: lock a PDF with Scansy

Scansy’s PDF tools work offline, so the file and its password never leave your phone.

  1. Open the PDF tools in Scansy and choose Lock PDF.
  2. Pick the document you want to protect.
  3. Enter a password (see the tips below) and save the locked copy.
  4. Test it. Open the locked file and confirm it asks for the password.
  5. Share the file through one channel and the password through another.

Need to protect several files at once, such as a year of statements? Use batch protect to password-protect multiple PDFs in one go. To remove a password you know, use Unlock PDF.

Choosing a strong password

Password-protected PDFs can be attacked offline by guessing passwords very quickly, so the password is the whole defence. Length matters far more than symbols.

  • Use a passphrase of four or more unrelated words, like “harbor-violet-tractor-lemon”. It’s long, and easy to read out loud.
  • Avoid personal details such as birthdays, names and phone numbers. Anyone who has the document may know them, because they’re often printed in it.
  • Don’t reuse an email or banking password.
  • Store it in a password manager, not in a note next to the file.

Sharing a locked PDF safely

The most common mistake is sending the password in the same email as the file. If that email is forwarded or the account is compromised, the password travels with it.

  • Send the file by email and the password by text message or a phone call.
  • Or agree on the password in person before you send anything.
  • Some organisations (banks, accountants) tell you which password format they use; follow their instructions so they can open the file.

What a password doesn’t do

A password protects the file in transit and at rest. It doesn’t stop someone who has the password from copying, printing or forwarding the contents, and it doesn’t protect the document while it’s open on screen. Keep that in mind for very sensitive documents: share them only with people who need them.

It’s also worth keeping an unlocked original on your phone, so a forgotten password doesn’t lock you out of your own document. Scansy keeps your documents on your device (see the privacy policy). For the full flow from paper to PDF, see how to scan documents to PDF on Android.