Thanks Emmanuel for the clarification.

I've now found an online converter for .tga and .dds files (I couldn't open them in Photoshop, apparently) and I managed to import some .obj files that had long resisted me!

I'm still stuck with a few .3ds downloaded from free repositories. I see the .3ds and the textures, but no .mtl file; is it missing and therefore it's a hopeless cause? I'll give you a specific example with this fireplace: https://open3dmodel.com/3d-models/firep ... _4902.html

As always, thanks a lot for the help!