Hello, if the file is on other format, try to import, select the type, then it s ok.
For the format, .obj is simple and more powerful, i think, because you can export model texture and armature, and it runs on all the programs ; 3ds max, blender, 3d game studio, daz 3d,...
3ds is fine but you need to press "smooth" after importing.
Fbx is ideal for architecture creation
Good trade