TGA format is used for raster graphics and OBJ format stores geometry or 3D meshes, so it is unlikely direct tga to obj conversion is doable.
What is possible though is to use a 3D modeling tool and use TGA texture on existing OBJ mesh to produce a 3D model, but saving it whole would require a different format, such as FBX or something similar.
Updated: November 2, 2023