This is possible because of the "Project to this PC" feature available on Windows for devices equipped with Miracast ...
Open Settings Select System settings Open Display settings Scroll down till you see Multiple Displays Locate Connect to a wireless display ... stream or duplicate my Windows computer on to Xbox ...
While originally designed as a remote access program, you can use Splashtop to turn your iPad into a secondary display for your Windows PC with a wired or wireless link. It's very similar to spacedesk ...