Protect PDF
Add AES-256 password encryption to your PDF and decide exactly what recipients may do with it. Everything happens on your own device.
- No uploads
- Runs locally
- No sign-up
Your files are processed locally in your browser — nothing is uploaded.
How to protect a PDF
- Add the PDF you want to protect by dragging it onto the upload area, or click to browse.
- Choose a password of at least 6 characters and enter it twice to confirm it.
- Set the permissions recipients get after opening the file — printing, copying, editing, and more.
- Click "Protect PDF" and download the encrypted file. Keep the password safe — there is no way to recover it.
Encrypt documents without revealing them — or the password
Password-protecting a PDF is usually the last step before sending something sensitive: a payslip to an employee, a bank statement to an accountant, a medical certificate to an insurer. Using a server-based tool for that final step defeats the purpose — the unprotected original travels across the internet, and you hand the chosen password to infrastructure you do not control. CoolPDF performs the encryption entirely on your device. The file is read locally, encrypted with AES-256 inside your browser tab, and saved straight back to your disk. The password you type never crosses the network — there is no server that could receive it. That makes the tool safe for confidential documents, even on a work laptop or public Wi-Fi. When you close the tab, both the file and the password are gone.
Frequently asked questions
How strong is the encryption?
CoolPDF uses AES-256, the strongest encryption defined by the PDF standard — the same grade used by government and banking applications. Without the password, the content cannot be read.
What happens if I forget the password?
There is no recovery option — that is the point of strong encryption. CoolPDF never sees or stores your password, so keep it somewhere safe, such as a password manager.
Are the permissions enforced by every PDF reader?
Compliant readers — including Adobe Acrobat, Chrome, and macOS Preview — respect the printing, copying, and editing restrictions. They are a policy mechanism rather than DRM, so treat them as a strong request, not a guarantee.
Read the full guide
How to Password Protect a PDF (AES-256)
CoolPDF is a free, browser-based PDF toolkit. Unlike traditional online PDF tools, CoolPDF processes all files locally on the user’s device using WebAssembly — files are never uploaded to any server. The tools require no account, no email, and no sign-up, and are completely free with no usage limits. This makes CoolPDF suitable for confidential documents such as contracts, medical records, and financial statements.