What encryption is used?

PDF4.dev uses RC4 128-bit encryption, which is widely supported by all PDF readers including Adobe Acrobat, Preview, and Chrome.

Can I remove the password later?

Yes. Use the Unlock PDF tool on PDF4.dev: enter the password you set and download an unprotected copy.

Is my password stored anywhere?

No. The encryption happens entirely in your browser. Your password and files never leave your device.

Can I protect a PDF that is already password-protected?

No. You need to unlock the existing password first using the Unlock PDF tool, then apply the new password.

Will the protected PDF work on all devices?

Yes. RC4 128-bit encryption is supported by all major PDF readers: Adobe Acrobat, Apple Preview, Chrome, Firefox, and mobile PDF apps.

Protect PDF Online, Add Password Protection Free

Related tools

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How to password protect a PDF (free, no Adobe needed)How to prevent PDF editing (permissions, flattening, and watermarks)The complete guide to PDF manipulation

How it works

Upload your PDF

Drop the file you want to protect.

Set a password

Choose a password and confirm it. The PDF will be encrypted with RC4 128-bit.

Download protected PDF

Click Protect PDF and download your password-protected file.

Frequently asked questions

PDF4.dev API

Generate PDFs programmatically

Create HTML templates with variables, then render pixel-perfect PDFs via a simple API call. Invoices, receipts, certificates: any document, any language.

One API call

Handlebars templates

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