There is only one file type that uses the .MSHC extension:
Microsoft Help Container File
Help package created in the MS Help Viewer 1.x format, which replaces the MS Help 2.x (.HXS) and MS Help 1.x (.CHM) formats; stores help content such as .HTML files, images, and written text; saved in a compressed .ZIP format.
MSHC files store help documents created for software applications. The documentation is deployed with software applications as a signed .CAB file that contains MSHC packages.
Updated: November 7, 2012