Password Protect PDF Online
Encrypt your PDF with standard password encryption to prevent unauthorized viewing.
Select PDF File
or drag & drop PDF here
About Protect PDF Online — Free Password Protection & AES Encryption
KAOpdf Protect PDF allows you to secure sensitive PDF documents by encrypting them with a custom password online for free. Whether you need to protect financial statements, legal contracts, confidential corporate documents, or private personal records, our tool applies industry-standard PDF encryption algorithms. Once protected, no one can view, print, or edit the file without entering your password. Everything is processed with maximum security, ensuring your files and passwords remain strictly confidential. 100% free, no software installation, and no watermark.
How to Use Protect PDF
Select PDF Document
Choose or drag and drop the PDF file you want to lock with a password from your device.
Set a Strong Password
Enter your desired password and confirm it. We recommend using a mix of letters, numbers, and symbols.
Encrypt and Download
Click "Protect PDF" to apply strong encryption, then instantly download your password-protected PDF file.
Specifications & System Limits
100% Client-Side Privacy
Files are processed entirely within your browser memory via WebAssembly. Your documents never touch external servers.
Super Fast & No Waiting
Instant high-speed conversion with ultra-low latency. Never wait in arbitrary processing queues.
100% Free & No Watermarks
All PDF tools are accessible free of charge without watermarks, hidden paywalls, or required registration.
Frequently Asked Questions (FAQ)
We utilize standard PDF security encryption standards. Once encrypted, the file cannot be viewed, printed, or extracted without the correct password.
No. For maximum security, we do not store your passwords on any server. If you forget the password, the PDF cannot be opened, so please keep a safe backup of your password.
Not at all. Password encryption only secures the document access permissions and does not alter text, images, tables, or document layout.
Yes. KAOpdf Protect PDF runs directly in any modern mobile browser without requiring app installations.
KAOpdf is 100% free with no hidden subscriptions, no watermarks, and no restrictions on the number of files you can protect.
Yes. If you know the password, you can easily remove the password protection anytime using our Unlock PDF tool.
Related PDF Tools
How was your experience using KAOpdf Protect PDF?
Give us a star rating or report any bugs you encountered with this tool.
About Protect PDF Online — Free Password Protection & AES Encryption
KAOpdf Protect PDF allows you to secure sensitive PDF documents by encrypting them with a custom password online for free. Whether you need to protect financial statements, legal contracts, confidential corporate documents, or private personal records, our tool applies industry-standard PDF encryption algorithms. Once protected, no one can view, print, or edit the file without entering your password. Everything is processed with maximum security, ensuring your files and passwords remain strictly confidential. 100% free, no software installation, and no watermark.
How to Use Protect PDF
Select PDF Document
Choose or drag and drop the PDF file you want to lock with a password from your device.
Set a Strong Password
Enter your desired password and confirm it. We recommend using a mix of letters, numbers, and symbols.
Encrypt and Download
Click "Protect PDF" to apply strong encryption, then instantly download your password-protected PDF file.
Specifications & System Limits
100% Client-Side Privacy
Files are processed entirely within your browser memory via WebAssembly. Your documents never touch external servers.
Super Fast & Reliable
Instant high-speed conversion with ultra-low latency. Never wait in arbitrary processing queues.
100% Free & No Watermark
All tools on KAOpdf are completely free with no watermarks, no file limits, and no account registration required.
Frequently Asked Questions (FAQ)
How secure is password protection in KAOpdf?+
We utilize standard PDF security encryption standards. Once encrypted, the file cannot be viewed, printed, or extracted without the correct password.
Can I recover a forgotten password?+
No. For maximum security, we do not store your passwords on any server. If you forget the password, the PDF cannot be opened, so please keep a safe backup of your password.
Does protecting a PDF reduce the file quality?+
Not at all. Password encryption only secures the document access permissions and does not alter text, images, tables, or document layout.
Can I protect PDF files on mobile devices (Android / iPhone)?+
Yes. KAOpdf Protect PDF runs directly in any modern mobile browser without requiring app installations.
Is there any cost or limit on file size?+
KAOpdf is 100% free with no hidden subscriptions, no watermarks, and no restrictions on the number of files you can protect.
Can I remove the password later?+
Yes. If you know the password, you can easily remove the password protection anytime using our Unlock PDF tool.