@pdfsmaller/pdf-decrypt

Full-featured PDF decryption with AES-256 and RC4 support. Built for browsers, Node.js 18+, Cloudflare Workers, and Deno.

Companion to @pdfsmaller/pdf-encrypt. Powers PDFSmaller.com's Unlock PDF tool.

Features

• AES-256 decryption (V=5, R=6) — PDF 2.0 standard
• RC4 40/128-bit decryption (V=1-2, R=2-3) — legacy support
• User + Owner passwords — accepts either password to decrypt
• Batched async decryption — processes thousands of objects without browser freeze
• Web Crypto API — no native dependencies, works everywhere
• Lightweight — ~18KB total (crypto + decryption logic)
• Zero dependencies — only pdf-lib as a peer dependency
• TypeScript types included

Installation

npm install @pdfsmaller/pdf-decrypt pdf-lib

Quick Start

import { decryptPDF } from '@pdfsmaller/pdf-decrypt';
import fs from 'fs';

const pdfBytes = fs.readFileSync('encrypted.pdf');
const decrypted = await decryptPDF(new Uint8Array(pdfBytes), 'my-password');
fs.writeFileSync('decrypted.pdf', decrypted);

API

decryptPDF(pdfBytes, password)

Decrypt a password-protected PDF. Supports both AES-256 and RC4 encryption — the algorithm is detected automatically.

| Parameter | Type | Description | |-----------|------|-------------| | pdfBytes | Uint8Array | The encrypted PDF file as bytes | | password | string | The user or owner password |

Returns: Promise<Uint8Array> — The decrypted PDF bytes

Throws:

• "This PDF is not encrypted" — if the PDF has no encryption dictionary
• "Incorrect password" — if neither user nor owner password matches
• "Unsupported encryption" — if the encryption version is not supported

isEncrypted(pdfBytes)

Check if a PDF is encrypted without attempting to decrypt it.

| Parameter | Type | Description | |-----------|------|-------------| | pdfBytes | Uint8Array | The PDF file as bytes |

Returns: Promise<{ encrypted: boolean, algorithm?: 'AES-256' | 'RC4', version?: number, revision?: number, keyLength?: number }>

Examples

Decrypt with Auto-Detection

import { decryptPDF, isEncrypted } from '@pdfsmaller/pdf-decrypt';

// Check encryption type first
const info = await isEncrypted(pdfBytes);
if (info.encrypted) {
  console.log(`Encrypted with ${info.algorithm}`);
  const decrypted = await decryptPDF(pdfBytes, password);
}

Roundtrip with @pdfsmaller/pdf-encrypt

import { encryptPDF } from '@pdfsmaller/pdf-encrypt';
import { decryptPDF } from '@pdfsmaller/pdf-decrypt';

// Encrypt
const encrypted = await encryptPDF(pdfBytes, 'secret');

// Decrypt
const decrypted = await decryptPDF(encrypted, 'secret');

Browser Usage

<input type="file" id="pdf-input" accept=".pdf" />
<input type="password" id="password" placeholder="Enter password" />
<button id="decrypt-btn">Decrypt</button>

<script type="module">
  import { decryptPDF } from '@pdfsmaller/pdf-decrypt';

  document.getElementById('decrypt-btn').addEventListener('click', async () => {
    const file = document.getElementById('pdf-input').files[0];
    const password = document.getElementById('password').value;
    const pdfBytes = new Uint8Array(await file.arrayBuffer());

    try {
      const decrypted = await decryptPDF(pdfBytes, password);

      // Download
      const blob = new Blob([decrypted], { type: 'application/pdf' });
      const url = URL.createObjectURL(blob);
      const a = document.createElement('a');
      a.href = url;
      a.download = 'decrypted.pdf';
      a.click();
    } catch (e) {
      alert(e.message);
    }
  });
</script>

Supported Encryption

| Algorithm | PDF Version | Key Length | Status | |-----------|-------------|-----------|--------| | AES-256 (V=5, R=6) | 2.0 (ISO 32000-2) | 256-bit | Supported | | RC4 (V=2, R=3) | 1.4+ (ISO 32000-1) | 128-bit | Supported | | RC4 (V=1, R=2) | 1.1+ | 40-bit | Supported | | AES-128 (V=4, R=4) | 1.6+ | 128-bit | Not yet supported |

Comparison with pdf-decrypt-lite

| Feature | pdf-decrypt | pdf-decrypt-lite | |---------|-------------|-----------------| | AES-256 | Yes | No | | RC4 128-bit | Yes | Yes | | RC4 40-bit | Yes | Yes | | Batched async | Yes | No (sync only) | | Size | ~18KB | ~8KB | | Use case | Full decryption | RC4-only, minimal |

Choose pdf-decrypt-lite if you only need RC4 and want the smallest possible bundle. Choose pdf-decrypt for full AES-256 + RC4 support.

Related Packages

| Package | Description | |---------|-------------| | @pdfsmaller/pdf-encrypt | Full encryption — AES-256 + RC4 (companion to this package) | | @pdfsmaller/pdf-encrypt-lite | Lightweight RC4-only encryption (~7KB) | | @pdfsmaller/pdf-decrypt-lite | Lightweight RC4-only decryption (~8KB) |

License

MIT — PDFSmaller.com