.CHM File Extension
Compiled HTML Help File
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What is a CHM file?
A CHM file contains help documentation compiled and saved in a compressed HTML format. It may include text, images, and hyperlinks. CHM files are used by Windows programs as an online help solution. They are compressed using LZX compression.
As help documentation has improved and progressed toward website and browser-based formats, the CHM format has largely been retired. Most programs no longer use CHM-based help documentation, and most programs that previously opened CHM files are either unmaintained or no longer open CHM files.
NOTE: While CHM files typically contain help documentation, some contain eBooks.
How to open a CHM file
In Windows, you can open a CHM file by double-clicking it. When you do, the CHM file will appear within Microsoft HTML Help Executable.
If your CHM file contains an eBook, you can open it in Calibre (multiplatform) or another eReader that supports the CHM format.