an .spp file is not a Substance Material file. It is a document from Substance Painter. They are useful for when you need to take a break from painting and come back to the file later to finish up.
To bring your painting and material work into C4D, you need to export your maps from Painter using the file--> export feature. You shouldn't need to export the mesh. Just the maps as I assume the mesh is already exported somewhere else since you were able to paint on it.