There is a text file which controls this setting. It is located in the game install directory.

1-Right click the game in your Steam library
2-Click properties
3-Click local files
4-Click browse local files
5-Open gamepad.txt
6-Typing "1" into the file will enable the gamepad/controller support but disable the advanced keyboard functionality / typing "0" into the file will enable the advanced keyboard functionality but disable the gamepad/controller support
7-Save the file
*8-You may need to set the game.exe to run as administrator for this to work (my main pc needed this)
*9-You may need to disable Steam input with your controller type by clicking Steam in the top left corner of the Steam window, click settings, click controller, and disable Steam input for your controller type (You can also do this for the individual game by right clicking on it and selecting properties and then controller and disabling Steam input for your controller type)
*10-Make sure your controller is set as your preferred device in windows. Right click your start menu and click search. Type in "Set up USB game controllers" (without the quotes) and click the app that comes up. Click advanced. Make sure the controller you want to use is selected in the window instead of "None". Click OK and you should be good to go!

While in game, you can now press F1 and it will open a dialogue window to customize the gamepad buttons. They are named according to an Xbox controller.

THE OTHER SETTINGS INSIDE THE DIALOGUE WINDOW ARE ENGINE DEFAULTS BUT SHOULD NOT BE MODIFIED AS THE GAME MAY BECOME UNSTABLE GIVEN THAT A LOT OF THEM ARE OVERWRITTEN BY THE GAME.