# PDF Comparison Tool

A comprehensive web-based tool for comparing PDF documents with advanced features including OCR validation, color difference detection, spelling verification, and barcode/QR code detection.

## Features

- **PDF Validation**: Ensures uploaded PDFs contain "50 Carroll" using OCR
- **Color Difference Detection**: Identifies visual differences between PDFs and highlights them with red boxes
- **Spelling Verification**: Checks text against both English and French dictionaries
- **Barcode/QR Code Detection**: Automatically detects and reads barcodes and QR codes
- **Visual Comparison**: Side-by-side comparison with annotated differences
- **Modern Web Interface**: Responsive design with Bootstrap and custom styling

## Requirements

### System Requirements
- Python 3.7 or higher
- macOS, Linux, or Windows
- Tesseract OCR engine (for text extraction)

### Python Dependencies
All dependencies are listed in `requirements.txt`:
- Flask (web framework)
- PyPDF2 (PDF processing)
- pdf2image (PDF to image conversion)
- OpenCV (image processing)
- pytesseract (OCR)
- pyzbar (barcode detection)
- pyspellchecker (spelling verification)
- scikit-image (image comparison)
- Pillow (image manipulation)

## Installation

### 1. Install Tesseract OCR

**macOS:**
```bash
brew install tesseract
```

**Ubuntu/Debian:**
```bash
sudo apt-get install tesseract-ocr
```

**Windows:**
Download from [Tesseract GitHub](https://github.com/UB-Mannheim/tesseract/wiki)

### 2. Install Python Dependencies

```bash
# Create virtual environment (recommended)
python -m venv venv
source venv/bin/activate  # On Windows: venv\Scripts\activate

# Install dependencies
pip install -r requirements.txt
```

### 3. Download Language Data (if needed)

The application will automatically download required NLTK data on first run.

## Usage

### 1. Start the Application

```bash
python app.py
```

The application will start on `http://localhost:5000`

### 2. Upload PDFs

1. Open your web browser and navigate to `http://localhost:5000`
2. Select two PDF files for comparison
3. Both PDFs must contain "50 Carroll" for validation
4. Click "Compare PDFs" to start the analysis

### 3. View Results

The comparison results are displayed in three tabs:

- **Visual Comparison**: Side-by-side view with red boxes highlighting differences
- **Spelling Issues**: Table of spelling errors with suggestions from English and French dictionaries
- **Barcodes & QR Codes**: List of detected barcodes with their data and positions

## File Structure

```
ProofCheck/
├── app.py                 # Main Flask application
├── pdf_comparator.py      # PDF comparison logic
├── requirements.txt       # Python dependencies
├── README.md             # This file
├── templates/
│   └── index.html        # Main web interface
├── static/
│   ├── css/
│   │   └── style.css     # Custom styles
│   ├── js/
│   │   └── script.js     # Frontend JavaScript
│   └── results/          # Generated comparison images
├── uploads/              # Temporary uploaded files
└── results/              # Comparison results JSON files
```

## How It Works

### 1. PDF Validation
- Converts PDF pages to images using `pdf2image`
- Uses Tesseract OCR to extract text
- Validates presence of "50 Carroll" in extracted text

### 2. Color Difference Detection
- Converts PDF pages to images
- Resizes images to same dimensions
- Uses structural similarity index (SSIM) to detect differences
- Draws red rectangles around detected differences

### 3. Spelling Verification
- Extracts text using OCR
- Splits text into individual words
- Checks each word against English and French dictionaries
- Provides spelling suggestions for incorrect words

### 4. Barcode/QR Code Detection
- Uses `pyzbar` library to detect barcodes and QR codes
- Extracts data and position information
- Displays results in organized table format

## Configuration

### Environment Variables
- `FLASK_ENV`: Set to `development` for debug mode
- `MAX_CONTENT_LENGTH`: Maximum file upload size (default: 16MB)

### Customization
- Modify `pdf_comparator.py` to change comparison algorithms
- Update `static/css/style.css` for custom styling
- Edit `templates/index.html` for interface changes

## Troubleshooting

### Common Issues

1. **Tesseract not found**
   - Ensure Tesseract is installed and in your system PATH
   - On macOS, try: `brew install tesseract`

2. **PDF processing errors**
   - Check that PDFs are not corrupted
   - Ensure PDFs contain readable text (not just images)

3. **Memory issues with large PDFs**
   - Reduce DPI in `pdf_comparator.py` (default: 200)
   - Process PDFs page by page for very large documents

4. **Spelling checker not working**
   - Ensure internet connection for first run (downloads dictionary data)
   - Check that `pyspellchecker` is properly installed

### Performance Tips

- Use smaller DPI values for faster processing
- Limit PDF page count for large documents
- Ensure sufficient RAM for image processing

## Security Considerations

- Uploaded files are stored temporarily and cleaned up
- File size limits prevent DoS attacks
- Input validation prevents malicious file uploads
- Session-based file handling ensures isolation

## Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests if applicable
5. Submit a pull request

## License

This project is open source and available under the MIT License.

## Support

For issues and questions:
1. Check the troubleshooting section
2. Review the code comments
3. Create an issue on the repository

## Future Enhancements

- Support for more document formats
- Advanced text comparison algorithms
- Machine learning-based difference detection
- Batch processing capabilities
- Export functionality for comparison reports