If you purchased Planetary Annihilation on the Uber Store or received a copy, go to My Keys and select your game key. Once the key is activated, you will be presented with an option to convert it to a Steam code. You can then enter this code into your Steam client as a “Activate a product on Steam.”

You won’t be able to re-convert your code back into a key. However, because your key is attached to your UberNet account, you’ll be able to play both via the Launcher and Steam.