From LightWiki

An Object is a 3D model of something and is one of Layout's four principle object types along with Bone, Light and Camera. Objects that can be loaded in LightWave are

• The native LWO format
• OBJ (although you may wish to get Dodgy's MTL import/export to help with texturing)
• 3DS - the old 3D Studio format limited to 64k polygons that must be triangles
• DXF a veritable workhorse of a format. It's old, there are loads of variations and LightWave does not support all the entities that can be held in a DXF but it is the lingua franca of 3D modelling

(Note: no format external to LightWave can handle LightWave subpatches or morphs)