HelpNDoc tool for making various help files uses .hnd files to store its projects. These projects can be exported and saved in all kinds of help files, including .chm files in Microsoft compiled HTML format. This seems to be the only way how to perform this conversion.
Convert HelpNDoc project file to Microsoft compiled HTML help module.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert hnd to chm on Windows
A set of tools used to write help files, manuals and documentation
Convert from hnd file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.