Full screen mode displays the active file using the whole screen. The ribbon / menu, toolbars, status bar and other dockable windows that would normally be displayed as part of the overall UltraEdit application window will be hidden while in this mode.
Once in full screen mode, a small window with an icon button will be shown to allow you to switch back to normal editing. Additionally, you can press the ESC key to exit full screen mode.
When exiting full screen mode, the main UltraEdit application window and all other windows will be returned to their previous state.
UltraEdit Wiki