There are 2 file types use the .MPX file extension:
2. Microsoft Project Exchange File
File exported by Microsoft Project, a project management application; saves the project plan in an ASCII text format instead of the .MPP binary format; designed for exchanging project data between different versions of Project as well as with third-party programs.
Several third-party programs can export and import MPX files. The MPXJ Java library can be used for implementing MPX import and export functionality in third-party applications.
Updated: May 31, 2015