pdf-encrypt-lite 🔒

Ultra-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!

🚀 Why pdf-encrypt-lite?

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.

The Problem We Solved:

• ❌ node-forge: 1.7MB minified
• ❌ crypto-js: 234KB (still too large with pdf-lib)
• ❌ Native crypto: Not available in many edge environments
• ✅ pdf-encrypt-lite: Only 7KB! 🎉

✨ Features

• 🔐 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

📥 Installation

npm install @pdfsmaller/pdf-encrypt-lite pdf-lib

💻 Usage

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();
}

🔥 Use Cases

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

🎯 Real-World Example

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!

🏗️ How It Works

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 🤯

📊 Comparison

| Library | Size | Real Encryption | Edge Compatible | |---------|------|-----------------|-----------------| | pdf-encrypt-lite | 7KB ✅ | ✅ | ✅ | | node-forge | 1,700KB | ✅ | ❌ | | crypto-js | 234KB | ✅ | ⚠️ | | pdf-lib alone | 0KB | ❌ | ✅ |

🤝 Contributing

We welcome contributions! This library powers PDFSmaller.com, so we maintain high standards for security and compatibility.

📜 License

MIT License - Use it freely in your projects!

🙏 Credits

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

🚀 Quick Start for Cloudflare Workers

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' }
    });
  }
}

📧 Support

• 🐛 Report issues
• 💡 Request features
• 🌐 Visit PDFSmaller.com
• 📧 Contact us

⭐ Star this repo if it helps you!

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