A File Source is simply a path to a file. In the File Source editor a filename is selected and the type of the file is selected.
File Source Types
Surfer Grid File (*.grd)
ArcInfo ASCII Grid File (*.asc)
3D Grid File (*.grd3)
Windows Bitmap (*.bmp)
JPEG Image (*.jpg)
3D Studio Max File (*.3ds)
GNU Triangulated Surface (*.gts)
Lightwave (*.lwo)
Milkshape (*.ms3d)
Normal Mapper (*.nmf)
NURBS (*.nurbs)
Wavefront (*.obj)
Triangular Irregular Network (*.tin)
Virtual Reality Model (*.wrl)