After you retarget the animation from C3D mocap data or from BVH or ASF mocap data (see Retargeting Mocap Data from C3D or BVH Files to a Rig), you can then save the resulting animation in a .motor file (normalized motion).
You can also animate a rig in any other way, such as with keyframes or action clips, and save that in a .motor file as well.
Saving animation and mocap data in .motor files makes it easy to build up a library of animation files that can then be applied to any tagged rig of the same structure (such as biped or quadruped).
To save animation data in a .motor file
Select an animated rig, making sure that it has been tagged. The rig can have mocap data applied to it or be animated in any other way, such as with keyframes.
Choose Tools 
MOTOR Save Motion from the Animate toolbar, or click the Save Motion button in the Mocap to Rig property editor.
In the Save Normalized Motion dialog box, set the Start and End values for the frames of the animation that you want to save in the file. Then click OK.
In the browser that appears, go to a folder where you want to keep the .motor file and enter a name for it. Then click OK to save it.