File menu > Save...
File toolbar > Save...
Save the model immediately
If you have not saved your model before now, the Save As... dialog-box opens.
MechDesigner saves two files with same file-name but different file-type. They are:
CXL is the file extension for the MechDesigner model.
MTD is the file extension for the MotionDesigner motions.
All of the motions name-tabs are saved to one file with this command.
If you want to save one motion to an MTD file, then use MotionDesigner > File toolbar > Save Active Motion .
Save Active Motion [MotionDesigner]