Importing and Exporting Models
The only program that can import and export model files from GTA V is ZModeler 3 (proprietary). The .yft file format is used for models, .ytd for texture archives.
ZModeler 3 provides basic modeling tools. However, any other software that allows exporting into a format that ZModeler 3 can import, such as .obj or .3ds, can be used. Many modelers use 3ds Max (proprietary) or Blender (free and open source), which have more advanced 3d creation tools compared to ZModeler.