Are you wondering what sort of file does 3D viewer use? Well, 3D viewers can support various file formats, including OBJ, STL, FBX, and more. These file formats are commonly used for 3D models and designs. OBJ files are frequently used for 3D printing and are supported by many 3D viewers. STL files are also popular in 3D printing and are compatible with most 3D viewers. Additionally, FBX files are widely used for 3D animation and can be opened with many 3D viewers as well. These file formats provide compatibility with different 3D software and enable users to view, manipulate and interact with 3D models effectively.