.gfx

.gfx files are uncompressed Autodesk Scaleform files. With a bit of editing, these can be opened and edited using SWF decompilers. Textures are loaded from an accompanied .wtd file with the same filename.

In GTA V, .gfx files are used for many things: in-game websites, mini-game menus, in-game phones, the HUD, heist menus, and more.

Editing as SWF

To edit a .gfx file without Autodesk, change the file's file extension to .swf. Then open it in a hex editor and change the header from GFX to FWS.

SouthernSanAndreasSuperAutos.com's ActionScript in SoThink.

You can now edit it with a SWF decompiling program, like JPEXS or SoThink.

When you're finished editing, change the header and file extension back.