What file formats can be used in UE4?

For example can we import t3d, obj (CAD) and other common file formats?

FBX is the main format, but version 4.2 will be adding .obj support

T3D is still doable, but if you’re trying to import from UE1/2 to UE4, it’s not likely to work without some work, due to fundamental changes. (Older Unreal Engines had you carving things out of an infinite solid; newer UE is pretty much the direct opposite.)