pdf-text-replace

Find and replace text in PDF files while preserving formatting.

Features

• Chainable API mimicking JavaScript's String.replace()
• Supports string and RegExp search patterns
• Preserves font styles, colors, and layout
• Handles FlateDecode compressed streams
• Graceful error handling (returns original buffer on failure)
• Automatic Unicode transliteration (CJK, Cyrillic, accented characters → ASCII)
• Pure TypeScript with minimal dependencies (pako for zlib, any-ascii for transliteration)

Installation

# From npm (when published)
npm install pdf-text-replace

# From local path
npm install /path/to/pdf-text-replace

Usage

import { PDF } from 'pdf-text-replace';
import { readFileSync, writeFileSync } from 'fs';

const input = readFileSync('document.pdf');

const modified = new PDF(input)
  .replace('John Doe', 'Jane Smith')
  .replace('[email protected]', '[email protected]')
  .replace(/\d{4}-\d{4}-\d{4}/g, 'XXXX-XXXX-XXXX')
  .toBuffer();

writeFileSync('modified.pdf', modified);

API

new PDF(input: Buffer | Uint8Array)

Create a new PDF instance from a buffer.

.replace(search: string | RegExp, replacement: string): this

Queue a text replacement operation. Returns this for chaining.

• search - String or RegExp pattern to find
• replacement - Text to replace matches with

.toBuffer(): Buffer

Apply all queued replacements and return the modified PDF as a Buffer.

Returns the original buffer unchanged if:

• No matches are found
• An error occurs during processing

How It Works

The library parses PDF content streams (both raw and FlateDecode compressed), finds text operators (Tj, TJ), and performs replacements while:

1. Preserving the original font and styling
2. Adjusting horizontal scaling (Tz operator) when replacement text has different width
3. Rebuilding the PDF with updated stream lengths and xref table

Unicode Support

Replacement text containing Unicode characters is automatically transliterated to ASCII for compatibility with standard PDF fonts (WinAnsiEncoding):

// Chinese → Pinyin
.replace('Author', '银宵')        // Becomes "YinXiao"

// Korean → Romanized  
.replace('Name', '스트레이')      // Becomes "seuteulei"

// Cyrillic → Latin
.replace('Hello', 'Привет')       // Becomes "Privet"

// Accented → Plain ASCII
.replace('Name', 'José García')   // Becomes "Jose Garcia"

This uses any-ascii for transliteration.

Limitations

• Only works with PDFs using WinAnsiEncoding (standard Latin text)
• Complex font encodings (CID, Identity-H) are not supported
• Unicode replacement text is transliterated to ASCII (original Unicode cannot be preserved)
• Text split across multiple operators may not be found
• Scanned/image-based PDFs cannot be modified

License

MIT