This article explains what CHW files are, their relationship to CHM files, and how to open them on your computer.
Remove File Type Associations to Default/None in Windows 10
A file with the CHW file extension is a compiled HTML Help index file. It is created when multiple CHM files are merged.
CHM files are help documents used by some programs to store questions and answers about how a program works or what various options mean. They are saved in HTML format, so they can contain text, hyperlinks, and images, and can generally be viewed in any Web browser.
These files are then used to maintain a table of contents of the information contained in the various CHM files, as well as references to the locations of the CHM files.