Create Photorealistic CAD Models

To create photorealistic models we use .gLTF file extension. glTF™ (GL Transmission Format) is a royalty-free specification for the efficient transmission and loading of 3D scenes and models by applications. glTF minimizes both the size of 3D assets, and the runtime processing needed to unpack and use those assets.
First you need to convert your CAD file into .obj or .stl file format, as described in this tutorial. Then you can simplify it, how-to in this tutorial.
You can edit your model with the software called Blender to make it more photorealistic. You can download it here: Blender is the free and open source 3D creation suite. It supports the entirety of the 3D pipeline—modeling, rigging, animation, simulation, rendering, compositing and motion tracking, even video editing and game creation.
Khronos group made a Blender glTF 2.0 Importer and Exporter Add-on. You can clone it from here: The Khronos glTF 2.0 importer and exporter is enabled by default in beta versions of Blender 2.8. If you have older version please use this ( repository or if you want to reinstall it copy the addons/io_scene_gltf2 folder into the scripts/addons/directory of the Blender installation, then enable it under the Add-ons tab. With this Add-on you can export Apertus ready gLTF files.