Protect PDF – Add Password to PDF Online Free
Lock your PDF with a password in seconds. Upload your file, set a password, and download a fully encrypted PDF — all in your browser.
Upload PDF to Protect
Drag & drop or browse files
Supports PDF up to 100MB
Max file size: 100 MB
How to Use
Upload PDF
Click or drag your PDF file into the upload area.
Set a Password
Enter and confirm your password. Minimum 4 characters.
Download Protected PDF
Click 'Protect PDF' and download your encrypted file.
Why Use Our Tool?
Client-Side Encryption
Your file is encrypted locally — it never touches our servers.
Universal Compatibility
Protected PDFs open in Acrobat, Preview, and all major viewers.
Instant & Free
No account, no payment — protect any PDF in seconds.
Content Preserved
Encryption only adds security — your PDF content is unchanged.
Frequently Asked Questions
What type of encryption is used?
pdf-lib applies RC4 128-bit encryption, which is compatible with all major PDF viewers including Adobe Acrobat, Preview, and browser-based readers.
What restrictions are added to the PDF?
Viewers can open and read the PDF with the password, and fill in forms. Copying text, editing content, and low-resolution printing are disabled.
Can I recover the password if I forget it?
No. The password is never stored on our servers (processing is entirely client-side). Keep your password safe — there is no recovery option.
Will the file content change?
No. Only security settings are added. The text, images, and layout of your PDF remain exactly the same.