Privacy & Safety

How to Password-Protect Any File (So It Opens Anywhere)

Lock tax papers, IDs and contracts with a password and AES-256 encryption, in a way the other person can open without installing anything.

By Nebula October 27, 2026 2 min read

Steel padlock locked around a stack of documents and a USB stick

Emailing a scan of your ID, a tax return or a signed contract as a plain attachment means it sits readable in inboxes, backups and cloud folders for years. Locking it with a password fixes that. The hard part is usually the other person: they shouldn't need special software or an account to open it.

That's why we built the free File Locker. It locks any file on your own device, and the locked copy opens with just the password. You choose between two formats.

Option 1: a self-unlocking file (works in any browser)

The locker turns your file into a single .html file. The recipient double-clicks it, it opens in their web browser (Chrome, Edge, Firefox or Safari), they type the password and save the original file. It works offline, and it never needs our website: the small unlock page travels inside the file itself.

This is the strongest option. Your password goes through 600,000 rounds of a deliberately slow scrambler before it becomes the key, so guessing passwords takes a very long time. The real file name is locked inside too.

One catch: some phones and email apps won't run an .html attachment. If that happens, the recipient can drop the file on the File Locker page under "Unlock a file" instead.

Option 2: a password zip (for 7-Zip, WinRAR and Keka)

Prefer a classic? The locker can also make an AES-256 encrypted .zip that opens in free unzip apps: 7-Zip or WinRAR on Windows, Keka or The Unarchiver on Mac, and most Android file managers.

Two things to know. Windows' and Mac's built-in unzip can't open strong zip passwords, so the other person may need one of those apps. And the zip format checks passwords much faster than the self-unlocking file does, so use a long password.

Step by step

Open the File Locker and drop in one or more files.
Pick Self-unlocking file or Password zip.
Type a password, or press Make a strong one and copy it somewhere safe.
Tick the box confirming you saved the password, then press Lock & download.
Send the locked file one way and the password another way, for example email for the file and a text message or phone call for the password.

The one rule: don't lose the password

There is no "forgot password" button. Your file and password never leave your device, so nobody, including us, can open a locked file without it. Save the password in a password manager before you lock anything important.

Why programs can only go in a zip

Scammers like to hide harmful downloads inside "secure document" web pages to slip them past email filters. To keep the locker from being used that way, programs, scripts and web pages can only be locked as a password zip.