Tachyon Space Technology

I'd like to create my own custom agency (i.e: C7 Aerospace, Kerbodyne, etc.), which have .dds files in the GameData/Squad/Agencies directory, but I don't know what program I need to use to view the .dds file format. Notepad just gave me a jumbled mess, so it's obviously more than just a config file I could copy, alter, and paste back into the directory. Any assistance here would be great. Thanks!