Add mandatory PATCH_PDFWRITER.md documentation

Complete mandatory documentation for PyPDF2 compatibility.
This package benefits from oca-ocb-base compatibility layer.

🤖 assisted by claude

odoo-bringout-oca-ocb-account_edi_ubl_cii/doc/PATCH_PDFWRITER.md

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+# PyPDF2 Compatibility Patch - Account EDI UBL CII (OCB)
+
+## Overview
+
+This package benefits from the PyPDF2 compatibility fixes implemented in the `oca-ocb-base` package. The account_edi_ubl_cii module uses `OdooPdfFileWriter` classes that are automatically compatible with PyPDF2 3.0.0+ through the main compatibility layer.
+
+## Problem
+
+In PyPDF2 3.0.0, several classes and methods were deprecated and removed:
+- `PdfFileWriter` → `PdfWriter`
+- `PdfFileReader` → `PdfReader`
+- `cloneReaderDocumentRoot()` → `clone_reader_document_root()`
+- Various other method names changed
+
+## Affected Functionality
+
+The account_edi_ubl_cii module uses PyPDF2 for:
+- UBL (Universal Business Language) invoice PDF generation
+- CII (Cross Industry Invoice) document processing
+- Electronic invoice XML embedding in PDFs
+- Standards-compliant electronic invoicing
+
+## Solution
+
+**This package requires NO direct patches** because it uses:
+1. `OdooPdfFileWriter` from `odoo.tools.pdf` (oca-ocb-base)
+2. `OdooPdfFileReader` from `odoo.tools.pdf` (oca-ocb-base)
+
+The main compatibility layer in `oca-ocb-base` handles all PyPDF2 version compatibility automatically.
+
+## Files Using PyPDF2
+
+### `account_edi_ubl_cii/models/ir_actions_report.py`
+- Uses `OdooPdfFileWriter` for standards-compliant PDF generation (automatically compatible)
+- Calls `writer.cloneReaderDocumentRoot(reader)`
+- Embeds UBL/CII XML in PDF documents
+
+## Implementation Details
+
+**No code changes needed** in this package. Compatibility is achieved through:
+
+1. **Dependency**: Requires `oca-ocb-base` with `pdfwrite` branch
+2. **Automatic compatibility**: `OdooPdfFileWriter` handles all PyPDF2 version differences
+3. **Standards compliance**: UBL/CII standards maintained through compatibility layer
+
+## Testing
+
+The compatibility has been verified with:
+- PyPDF2 3.0.0+ (new API)
+- PyPDF2 2.x (old API)
+- UBL invoice PDF generation
+- CII document processing
+- XML embedding in compliance documents
+
+## Branch Information
+
+- **Branch**: `pdfwrite`
+- **Based on**: Current master branch
+- **Type**: Dependency compatibility (no direct patches)
+- **Impact**: Automatic compatibility through oca-ocb-base dependency
+
+## Dependencies
+
+**CRITICAL**: This package requires:
+- `oca-ocb-base` package on `pdfwrite` branch
+- The main PyPDF2 compatibility layer must be active
+
+## Standards Compliance
+
+This patch maintains compliance with:
+- **UBL 2.1**: Universal Business Language standard
+- **CII D16B**: Cross Industry Invoice standard
+- **EN 16931**: European electronic invoicing standard
+- **PDF/A-3**: Long-term archival PDF format
+
+## Author
+
+- **Developer**: Ernad Husremović (hernad@bring.out.ba)
+- **Company**: bring.out.doo Sarajevo
+- **Date**: 2025-09-02
+
+## Related Issues
+
+This documentation addresses PyPDF2 compatibility for:
+- UBL electronic invoicing
+- CII standard compliance
+- European electronic invoicing (EN 16931)
+- B2B/B2G electronic document exchange
+
+## Installation
+
+1. Ensure `oca-ocb-base` is using the `pdfwrite` branch
+2. Use this package's `pdfwrite` branch (for documentation compliance)
+3. No additional installation steps required
+
+## Future Considerations
+
+- Monitor oca-ocb-base compatibility updates
+- Test UBL/CII workflows with future PyPDF2 versions
+- Ensure continued standards compliance with PDF changes