Ultra-lightweight PDF encryption (7KB) with real RC4 128-bit encryption. Built for edge environments like Cloudflare Workers. Powers PDFSmaller.com's encryption.
npm install @pdfsmaller/pdf-encrypt-liteUltra-lightweight PDF encryption library (only 7KB!) with real RC4 128-bit encryption
Built by PDFSmaller.com - Try our free online PDF tools with this encryption built-in!
When building PDFSmaller.com, we needed real PDF encryption that worked within Cloudflare Workers' 1MB limit. Every existing solution was 2-20MB+ in size. We were told it was "impossible" to implement proper PDF encryption in such a small package.
We proved them wrong.
This library is the exact encryption engine that powers PDFSmaller.com's Protect PDF tool - battle-tested on thousands of PDFs daily.
- 🔐 Real PDF encryption - RC4 128-bit encryption that actually works
- 📦 Tiny size - Only ~7KB total (MD5 + RC4 implementations)
- ⚡ Edge-ready - Works in Cloudflare Workers, Vercel Edge, Deno Deploy
- 🌐 Browser compatible - No Node.js dependencies
- 📱 Password protection - PDFs prompt for password in any reader
- 🛡️ PDF Standard compliant - Implements Algorithm 2 & 3 from PDF spec
- 🚀 Zero dependencies - Just needs pdf-lib as peer dependency
``bash`
npm install @pdfsmaller/pdf-encrypt-lite pdf-lib
`javascript
import { encryptPDF } from '@pdfsmaller/pdf-encrypt-lite';
import { PDFDocument } from 'pdf-lib';
// Basic usage
const encryptedPdfBytes = await encryptPDF(existingPdfBytes, 'user-password');
// With separate owner password
const encryptedPdfBytes = await encryptPDF(
existingPdfBytes,
'user-password',
'owner-password'
);
// Full example
async function protectPDF() {
// Load your PDF
const existingPdfBytes = await fetch('document.pdf').then(res => res.arrayBuffer());
// Encrypt it with pdf-encrypt-lite
const encryptedBytes = await encryptPDF(
new Uint8Array(existingPdfBytes),
'secret123',
'owner456'
);
// Save the encrypted PDF
const blob = new Blob([encryptedBytes], { type: 'application/pdf' });
const url = URL.createObjectURL(blob);
const a = document.createElement('a');
a.href = url;
a.download = 'protected.pdf';
a.click();
}
`
Perfect for:
- Edge Functions (Cloudflare Workers, Vercel Edge, Netlify Edge)
- Browser applications (Like PDFSmaller.com)
- Serverless functions with size limits
- Client-side PDF protection without server uploads
- Lightweight Node.js applications
See it in action at PDFSmaller.com/protect-pdf - our free online tool uses this exact library to encrypt PDFs directly in your browser. No uploads, no server processing, just pure client-side encryption!
We built custom implementations of:
1. MD5 hashing - For password processing per PDF spec
2. RC4 encryption - For content encryption
3. PDF object traversal - Encrypts all strings and streams
4. Standard Security Handler - Implements PDF encryption spec
Total size: ~7KB 🤯
| Library | Size | Real Encryption | Edge Compatible |
|---------|------|-----------------|-----------------|
| pdf-encrypt-lite | 7KB ✅ | ✅ | ✅ |
| node-forge | 1,700KB | ✅ | ❌ |
| crypto-js | 234KB | ✅ | ⚠️ |
| pdf-lib alone | 0KB | ❌ | ✅ |
We welcome contributions! This library powers PDFSmaller.com, so we maintain high standards for security and compatibility.
MIT License - Use it freely in your projects!
Built with ❤️ by PDFSmaller.com - Your free PDF toolkit
If this library helps you, check out our other free PDF tools:
- Compress PDF - Reduce PDF size by up to 90%
- Merge PDF - Combine multiple PDFs
- Split PDF - Extract pages from PDFs
- Protect PDF - Uses this library!
- 20+ more tools - All free, all private
`javascript``
export default {
async fetch(request, env) {
const formData = await request.formData();
const file = formData.get('pdf');
const password = formData.get('password');
const pdfBytes = new Uint8Array(await file.arrayBuffer());
const encrypted = await encryptPDF(pdfBytes, password);
return new Response(encrypted, {
headers: { 'Content-Type': 'application/pdf' }
});
}
}
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