FileInfo.com - The File Extensions Resource

.HMX File Extension

File Type	Help & Manual 4 Project
File Format	File
Common?	No
File Description	Windows help documentation created by Help & Manual authoring tool; formatted as XML files; can be output to HTML Help, Cross-platform Help, PDF, Visual Studio Help, Winhelp, Word documents, e-Books, or Print manuals
Program(s) that open hmx files	Windows: EC Software Help and Manual 4 or later

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/hmx