You can open .fbx, .bvh, .htr, .trc, .amc, and .c3d files with the File > Motion File Import method.
To open a motion file:
- Select File > Motion File Import from the MotionBuilder menu bar.
The Import Files dialog box appears.
- Navigate via the Import Files dialog, and select the file to import.
- Click Open.
The Import Options dialog box appears.
- Disable any elements of the file you do not want to load with the file.
- Click Import.
The file loads in MotionBuilder.