Help & Manual documentation tool and content management system uses several project formats, including .hmxz (compressed XML variant) and .hm3 (perhaps from version 3). There are no information available whenever you can simply resave one ot another, but it seems like the original software is the only choice here.
Convert Help & Manual help file compressed XML project to Help & Manual help file project.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert hmxz to hm3 on Windows
A multi-author documentation and content management system tool
Convert from hmxz 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.