CHM to Markdown Converter

CHM to Markdown Converter

A Python utility for converting Compiled HTML Help (.chm) files into clean Markdown, with built-in support for multiple document types through a profile system.

Originally built for Autodesk Revit API documentation; the generic profile works with any CHM file.

Features

• Profile-based conversion — generic profile for any CHM, revit profile for Autodesk Revit API docs
• Auto encoding detection — handles UTF-8, GB18030, GBK, GB2312, and more via chardet
• Cross-platform 7-Zip detection — finds 7z/7za/7zz on PATH (Windows, Linux, macOS)
• Flexible CHM structure support — handles html/ subdirectory, flat, and deeply nested layouts (e.g. DirectX SDK)
• --preserve-structure — optionally mirrors the CHM's internal folder hierarchy in the output instead of flattening everything into data/
• Code block preservation — detects language from class names and named divs; supports C#, VB, C++, F#, Python, Java, JS/TS, Bash, SQL, XML, JSON
• Table normalization — cleans and re-formats Markdown tables
• Index generation — produces file_index.json, id_lookup.json, and index.md for search and AI integration
• Async + batched processing — bounded concurrency and periodic GC prevent memory overflow on large CHM files (6 000+ pages)

Project Structure

chm_converter/           # Core package
├── config.py            # ConversionConfig dataclass + built-in profiles
├── encoding.py          # Encoding detection (chardet + CJK fallbacks)
├── extractor.py         # CHM extraction via 7-Zip; HTML folder detection
├── html_processor.py    # HTML cleaning, link rewriting, code block extraction
├── md_converter.py      # HTML → Markdown conversion + post-processing
├── indexer.py           # File dictionary building + index file generation
└── pipeline.py          # High-level async pipeline (process_chm_file, process_all_chm_files)

chm_to_markdown.py       # CLI entry point
resources/               # Place CHM files here
output/                  # Generated Markdown (created automatically)

Output layout

output/
└── <name>/
    ├── core/
    │   ├── file_index.json   # id → {title, filename, version}
    │   ├── id_lookup.json    # lowercase id → {title, filename, keywords, version}
    │   └── index.md          # alphabetical navigation page
    └── data/
        ├── Topic1.md
        ├── Topic2.md
        └── ...

Requirements

• Python 3.10+
• 7-Zip — 7z must be reachable via the default install path or PATH
  • Windows: installs to C:\Program Files\7-Zip\7z.exe by default, or add to PATH
  • Linux: sudo apt install p7zip-full
  • macOS: brew install p7zip

Installation

git clone https://github.com/DTDucas/chm-converter.git
cd chm-converter
pip install -r requirements.txt

Usage

Place .chm files in the resources/ folder, then run:

# Interactive menu (lists available CHM files)
python chm_to_markdown.py

# Convert a single file
python chm_to_markdown.py --single resources/docs.chm

# Convert all CHM files in resources/
python chm_to_markdown.py --all

# Use the Revit API profile (strips Revit help-viewer boilerplate)
python chm_to_markdown.py --all --profile revit

# Preserve the original folder hierarchy inside data/ (e.g. for DirectX SDK)
python chm_to_markdown.py --single resources/directx_sdk.chm --preserve-structure

# Keep extracted HTML for debugging
python chm_to_markdown.py --single resources/docs.chm --keep-html

# Tune performance
python chm_to_markdown.py --all --workers 4 --batch-size 25 --semaphore 10

CLI arguments

Argument	Short	Default	Description
--single FILE	-s	—	Convert a single CHM file
--all	-a	—	Convert all CHM files in resources/
--profile	-p	generic	Conversion profile: generic or revit
--keep-html	-k	off	Retain extracted HTML after conversion
--workers N	-w	8	Thread-pool size for CPU-bound conversion
--batch-size N	-b	50	Files processed per async batch
--semaphore N	—	20	Max concurrent I/O operations
--preserve-structure	—	off	Mirror CHM folder hierarchy in data/; preserve relative links

Profiles

Profile	Description
generic	Minimal cleanup — works with any CHM file
revit	Strips Autodesk Revit help-viewer UI chrome (collapsible regions, feedback links, code-tab toolbars, boilerplate text)

Custom profiles can be created programmatically:

from chm_converter.config import ConversionConfig
from chm_converter.pipeline import process_chm_file
import asyncio

cfg = ConversionConfig(
    classes_to_remove=["my-nav-bar", "site-footer"],
    ids_to_remove=["cookie-banner"],
    cleanup_patterns=[
        (r"Rate this article.*?---", "---"),
    ],
)

asyncio.run(process_chm_file("docs.chm", "extracted", "output", cfg=cfg))

AI Integration

The core/ folder is designed for RAG and AI search pipelines:

• file_index.json — maps every file ID to its title, filename, and version
• id_lookup.json — lowercase-keyed with extracted keyword lists for full-text search
• index.md — human-readable alphabetical index with anchor links

Troubleshooting

Problem	Solution
7z not found	Install 7-Zip and ensure it is on PATH; see Requirements above
Empty output / No HTML files found	CHM uses a nested folder layout — add --preserve-structure to enable recursive traversal
Revit 2025+ pages contain only a title, no body	Fixed in current version: TopicContent is no longer stripped from the Revit profile
Garbled CJK text	The tool auto-detects encoding via chardet; try --profile generic if issues persist
Memory errors on large CHM	Reduce --workers and --batch-size
Permission errors	Run the terminal with administrator / sudo privileges

License

MIT License

Author

Duong Tran Quang (DTDucas) [email protected] github.com/DTDucas Author: dtducas.com

Contributors

• Jiangxumin — Chinese encoding support, cross-platform 7-Zip detection, memory-safe batch processing (PR #11)