Add missing PATCH_PDFWRITER.md documentation

Complete mandatory documentation for PyPDF2 compatibility patch.

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odoo-bringout-oca-reporting-engine-report_qweb_pdf_cover/doc/PATCH_PDFWRITER.md

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+# PyPDF2 Compatibility Patch - Report QWeb PDF Cover
+
+## Overview
+
+This patch addresses the PyPDF2 deprecation error in the report_qweb_pdf_cover module when using PyPDF2 version 3.0.0 or higher. The original error was:
+
+```
+PyPDF2.errors.DeprecationError: PdfFileWriter is deprecated and was removed in PyPDF2 3.0.0. Use PdfWriter instead.
+```
+
+## Problem
+
+In PyPDF2 3.0.0, several classes and methods were deprecated and removed:
+- `PdfFileWriter` → `PdfWriter`
+- `PdfFileReader` → `PdfReader` 
+
+## Affected Functionality
+
+The report_qweb_pdf_cover module uses PyPDF2 for:
+- Adding front and back covers to PDF reports
+- PDF page manipulation and insertion
+- Cover page validation and processing
+- Comprehensive report formatting with covers
+
+## Solution
+
+This patch provides backward compatibility by creating a simple import compatibility layer that:
+1. Attempts to import from the new PyPDF2 API (`PdfWriter`, `PdfReader`)
+2. Falls back to the old API for older PyPDF2 versions
+3. Maintains full functionality without code changes
+
+## Files Modified
+
+### `report_qweb_pdf_cover/models/ir_actions_report.py`
+- Added compatibility import logic for basic PyPDF2 class imports
+- Maintains existing functionality without method wrapper requirements
+
+## Implementation Details
+
+### Compatibility Import Pattern
+```python
+try:
+    from PyPDF2 import PdfWriter as PdfFileWriter, PdfReader as PdfFileReader
+except ImportError:
+    # Fallback to old API for older PyPDF2 versions
+    from PyPDF2 import PdfFileWriter, PdfFileReader
+```
+
+## Usage Example
+
+The module allows adding covers to reports:
+
+```python
+# In Odoo report configuration
+report.pdf_front_cover = base64_encoded_pdf_cover
+report.pdf_back_cover = base64_encoded_pdf_cover
+
+# Generated report will include covers
+```
+
+## Functionality Features
+
+- **Front Cover Support**: Add custom front covers to reports
+- **Back Cover Support**: Add custom back covers to reports  
+- **Cover Validation**: Validates PDF cover files before processing
+- **Page Management**: Handles complex page insertion logic
+- **Error Handling**: Graceful degradation when covers are invalid
+
+## Testing
+
+The patch has been tested with:
+- PyPDF2 3.0.0+ (new API)
+- PyPDF2 2.x (old API via fallback)
+- Front cover attachment
+- Back cover attachment
+- Cover validation workflows
+
+## Branch Information
+
+- **Branch**: `pdfwrite`
+- **Based on**: Current master branch
+- **Type**: Compatibility patch
+- **Impact**: Backward compatible - no breaking changes
+
+## Author
+
+- **Developer**: Ernad Husremović (hernad@bring.out.ba)
+- **Company**: bring.out.doo Sarajevo
+- **Date**: 2025-09-02
+
+## Related Issues
+
+This patch resolves the PyPDF2 deprecation error encountered in:
+- PDF cover page insertion
+- Report formatting with covers
+- Custom branded document generation
+
+## Installation
+
+This patch is automatically applied when using the `pdfwrite` branch. No additional installation steps required.
+
+## Dependencies
+
+- Compatible with custom PDF covers
+- Maintains cover validation functionality
+- Works with existing cover configuration
+
+## Future Considerations
+
+While this patch provides immediate compatibility, consider:
+1. Eventually migrating to the new PyPDF2 API directly
+2. Testing cover functionality with future PyPDF2 versions
+3. Enhancing cover validation and error handling