A .vvd file is only one part of a Source Engine model. It contains the vertex data (geometry), but it requires the .mdl (model structure) and .vtx (hardware optimization/LODs) files to function correctly. You cannot convert a standalone .vvd effectively without the accompanying files in the same folder.
Converting VVD data—common in volumetric imaging, scientific visualization, or specialized game engine data—to a 3D polygon mesh ( vvd to obj extra quality