Converting a VTX file to FBX is not for the faint of heart. It requires a mental shift from "direct conversion" to "decompilation and reassembly." You need Crowbar to break the MDL, Noesis or Blender to interpret the SMD, and manual artistry to fix the materials.
: Used by the Source Engine (found in games like Half-Life 2 or Portal 2 ), VTX files store hardware-optimized material and mesh information. They rarely exist alone and are usually accompanied by .mdl (model structure) and .vvd (vertex data) files. vtx to fbx