The Pad2Key functionality enables the creation of a "per-game" controller to keyboard keys mapping, this is mostly used for old computers and old Windows games that are not compatible with a Gamepad.
You can create a pad2key profile for a system or for a specific game.
Select EDIT PADTOKEY PROFILE.
Select the keys from your controller to assign to a keyboard button and press
, a virtual keyboard will appear.
Select the keyboard key to affect to the pad button and repeat for all required buttons
Once done, SAVE.
The Pad2Key file is located near the game rom and has the same name as the game ROM with a .keys extension.
Here is an example of a .keys file content