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Password Protect a PDF

You need to email a tax return, share a medical report, or send a contract — but first, you want to lock it with a password so only the intended recipient can open it.

Here is the problem with most "protect PDF" tools: you upload your unencrypted document to their server, type your password into their form, and trust that they will encrypt it and forget both. That defeats the entire purpose of encryption. Your sensitive file and your password were both exposed to a third party.

KuroPDF encrypts your PDF entirely in your browser using a WebAssembly build of qpdf — the same battle-tested library used in enterprise document workflows. Your file is never uploaded. Your password is never transmitted. The encryption runs on your device and the encrypted output downloads directly.

You can choose between AES-256 (recommended for maximum security), AES-128 (compatible with older readers), or RC4-40 (legacy only — not secure, but required by some ancient systems). You can also set granular permissions: allow or block printing, copying text, editing, and form filling independently.

The result is a standards-compliant encrypted PDF that opens in any PDF reader. Share it via email, Slack, or cloud storage, and only people with the password can access the contents.

Open the Protect PDF tool →
  • Files never leave your device
  • No size limits
  • Free, no sign-up

How to password protect a pdf

  1. 1
    Drop your PDF

    Load the PDF you want to protect. It is parsed locally — your unencrypted document never touches a server.

  2. 2
    Set a strong password

    Enter a password. Use something long and unpredictable. The tool shows password strength. Consider a passphrase like "correct-horse-battery-staple" for memorability.

  3. 3
    Choose encryption level

    Select AES-256 for maximum security (default), AES-128 for wider compatibility, or configure permissions (print, copy, edit) independently.

  4. 4
    Download the encrypted PDF

    Click protect. The encrypted file downloads immediately. Share it via any channel — only the password holder can open it.

Frequently asked questions

How strong is the encryption?

AES-256 is the gold standard used by governments, military, and financial institutions worldwide. It is computationally infeasible to crack with current or foreseeable technology.

Does my password get sent anywhere?

No. Encryption runs entirely in your browser via WebAssembly. The password and file never leave your device. There is no server involved in the process.

Can I set different permissions (print, copy, edit)?

Yes — you can independently allow or block printing, text copying, editing, form filling, and annotation. These permissions are enforced by PDF readers that respect the standard.

Will the recipient need special software to open it?

No. Any standard PDF reader (Adobe Reader, Preview, Chrome, Firefox) can open password-protected PDFs. The recipient just needs the password you share with them.

Can I also remove a password from a PDF?

Yes — the same tool can decrypt a PDF if you know the current password. Enter the existing password and download an unlocked copy.

Is AES-256 compatible with all PDF readers?

AES-256 works in Adobe Reader 9+ and all modern readers (2008 onwards). For older software, use AES-128 or RC4-40 — though RC4 is no longer considered secure.

The real difference

Why KuroPDF exists

Every other PDF tool uploads your files to their servers. We think that is broken. Here is what we do differently - and what the alternatives actually cost you.

Nothing leaves your device

Files are processed in your browser using WebAssembly. Open DevTools → Network tab and verify: zero upload requests. Ever.

What competitors do instead:

Smallpdf, iLovePDF, and Adobe Acrobat all upload your files to their servers - your contracts, bank statements, and medical records pass through third-party infrastructure.

No file size limits, no daily caps

Process a 500-page PDF or batch-convert 200 photos. No cap, no throttle, no upgrade wall. Your device is the only limit.

What competitors do instead:

Smallpdf limits free users to 2 tasks per day. iLovePDF caps file sizes at 100MB. Adobe requires a $19.99/mo subscription for basic features.

Works completely offline

Install KuroPDF as a progressive web app. After the first visit, every tool works with zero internet - on a plane, in a bunker, wherever.

What competitors do instead:

Every cloud-based PDF tool stops working the moment your Wi-Fi drops. No connection = no work.

Real encryption, not security theatre

Password protection uses AES-256 encryption via a WebAssembly build of qpdf. The password never leaves your machine - there is no server to intercept it.

What competitors do instead:

When you 'protect' a PDF on Smallpdf or iLovePDF, your unencrypted file and password travel to their server, get processed, then get sent back. That is not security.

Free forever, no account needed

No login wall, no email harvesting, no 'continue with Google' popup. Open the site, use the tool, close the tab. Done.

What competitors do instead:

Adobe charges $239/yr. Smallpdf charges $108/yr. iLovePDF charges $84/yr. All require account creation to use basic tools.

Professional-grade codecs

MozJPEG for JPEG, OxiPNG for PNG, AVIF and WebP encoders - the same codecs used by Google and Mozilla. Not generic re-encoding.

What competitors do instead:

Most cloud tools use basic server-side encoders with less optimization control. You get worse compression at lower quality.

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