The emulator will prompt you to create the xinput1_3.dll file.
If you have found yourself downloading the file in 2021 or later, you are likely trying to solve a very specific problem: getting an older DirectInput controller (like a Logitech Rumblepad or an older generic gamepad) to work with a game that strictly requires XInput (Xbox 360 controllers). x360celib64r848vs2010zip link 2021