Question: how to open gltf files?
Answer: Open-source glTF converters are available from COLLADA, FBX, and OBJ. Assimp can import and export glTF. glTF files can also be directly exported from a variety of 3D editors, such as Blender, Vectary, Autodesk 3ds Max (using Verge3D exporter), Autodesk Maya, Modo, Paint 3D, and Substance Painter.