Can I save files on my D (Recovery) Drive ?

bad idea, it may interfere with a future recovery! although it is possible to open it and view files and save what ever you want, its better to do it on you home drive. if your home drive is running out of space try this program called, CCleaner (http://www.ccleaner.com/) (its free), and it will remove on those temporary garbage files on your pc also try getting an external drive to save large documents and movies that you wont use much on your pc in the external drive that will be connected to your pc (its almost like another hard drive) either way, try one or both it will help, just don't ever touch your recover drive!