If you don't want to bother with installing AutoHotkey, creating files, copy and pasting bits of code (see ABOVE), then just download and run this file...
WGT Golf Fullscreen.exe (810KB)
Allows you to use your other game apps without the game disappearing.
The keyboard shortcuts are the same as ABOVE...
CTRL + f
For fullscreen, you may have to hit the ' f ' key two or three times to get the game into fullscreen without its border.
CTRL + w
Puts the game back into windowed mode.
CTRL + x
Exits the script and turns off the shortcut keys. Does not change the game screen mode you are currently in.
You can close out the script once you have got the game into fullscreen mode if you wish. Its only purpose is to resize the game screen, it does not have to be running all the time you are playing, but if you exit the script you won't be able to resize the game screen with the shortcut keys.