RTTEX files are texture containers used by Rockstar’s RAGE Engine. Unlike standard images, you can’t just rename them. To view or edit these textures, you need to convert them to PNG. Here’s the fastest method.
Unzip the contents into a folder, e.g., C:\RTTEX_Tools\ . You should see RTTexConverter.exe and possibly a GUI.exe . rttex to png
Pros: No installation required. Cons: Not good for batch converting hundreds of files; requires uploading files to a third party. RTTEX files are texture containers used by Rockstar’s
Here is an interesting and informative post structure you can use: rttex to png