This tool can convert your .tex and .dds files to the same format and allows you to edit your textures with the help of a photoshop plugin like Intel Texture workshop or Nvidia texture tool to edit, or use any other program that supports .dds files like GIMP.

This is an open source project that can be found on GitHub. 
The source code is available for you to edit, create your own version of the app, or make a pull request to the main repository.

It is developed based on the .net framework 4.0.