obj to c3d conversion is most likely related to export or conversion of 3D models between classic 3D object files (.obj) and a specific 3D biomechanics format (.c3d), typically in effort to use the OBJ format as basis for making new animation.
Blender supports export of animations to several formats, including C3D, which means this feels like obvious choice how to achieve such export.
Updated: October 30, 2023