Protect PDF
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Protecting a PDF means applying password-based encryption and permission limits so the file cannot be opened, printed, copied, or edited without authorization. An open password gates viewing; permission flags restrict what a reader can do once inside. LittlePDF applies AES-256 through the PDF standard security handler, locking the file before you download it.
At a Glance
1 Credit
Per Protect
On-Device
Processing
AES-256
Encryption
25 MB
Free File Limit
Key Facts
LittlePDF Protect PDF applies AES-256 encryption (the PDF 2.0 / R6 standard security handler) entirely client-side in the browser, using qpdf compiled to WebAssembly.
Users can set an open password to gate viewing plus permission restrictions on printing, copying, and editing; the password is never uploaded, logged, or stored.
Each protect costs 1 credit; free accounts get 500 credits per day and a 25 MB file limit, while Pro supports files up to 500 MB.
How to Protect PDF in 3 Steps
Drop the PDF you want to protect into the upload area, or click to browse.
Set a document password, confirm it, and pick any permission limits you want to add.
Click Protect and download the password-protected copy.
Why Protect PDF with LittlePDF?
Encryption is applied in your browser, so neither the document nor the password is uploaded.
Set an open password to gate viewing and add limits on printing, copying, or editing on top.
The protected file uses AES-256, the PDF 2.0 standard, and opens with a password prompt in Acrobat, Preview, Chrome, and other current readers.
One credit per file against 500 free credits a day keeps routine protection effectively free.
Features
AES-256 Encryption
Protection uses the PDF standard security handler with AES-256, the R6 scheme defined in PDF 2.0 and supported since Acrobat X. The locked file prompts for a password in Acrobat, Preview, Chrome, and other current viewers without special software.
Open Password and Permissions
Require a password before the file will open, and optionally restrict printing, copying, and editing. The two layers combine, so you can let someone read a document while still blocking them from copying its text.
Locked on Your Device
The password is turned into a key and the file encrypted entirely in your browser. No credential or document content ever leaves your machine, so even a sensitive file is secured without trusting a server.
Frequently Asked Questions
Last updated: June 2026