A project file holds information about the video, pictures, and audio files that you have added in Windows DVD Maker and would like to burn to a DVD. This project file also includes information on the arrangement of those items as they will appear on the burned DVD, as well as information about the menu for the DVD.
You can save a project for a work in progress or for a DVD that you have already burned in Windows DVD Maker (as long as you save the project before closing Windows DVD Maker). Either way, you can open the saved project later on and burn it to a DVD. If you want, you can open a saved project, add additional items in Windows DVD Maker, and then burn the updated project to a DVD.
On the Add pictures and video to the DVD page in Windows DVD Maker, click File, and then click a Windows DVD Maker project file (at the bottom of the File menu) that you recently saved and want to open.