From Valve Developer Community
An older but functional version of this program is still available here. To use this version directly, place the VTF file to convert in the same directory with
vtf2tga.exe application, and in the command prompt type:
vtf2tga <Your VTF file to convert> <The resulting TGA file name>
- VTFEdit - a more flexible third-party alternative to VTF2TGA.