MSJ filename extension is associated with MicroSurvey CAD, a CAD software developed by MicroSurvey Software Inc. It is similar to the popular AutoCAD software tool.

MSJ files store temporary data used by the program, generated during information processing or other processes. MSJ files are saved in MSJ folder on the disk. After the processes that used MSJ files are complete, the files are compressed into MSD files and the MSJ folder is removed from disk.