Write data on the computer with Arduino
The keyboard library just sends key presses to the computer like a keyboard.  From the PCs point of view it's no different from you banging on the keyboard in front of it.  The Arduino can't control anything on the computer and it can't run any code on the computer.  Now if you can do what you want completely from the keyboard then arduino could send those same keypresses.  But the Arduino has no access to the PCs operating system or file system.