Select Close All in the File menu to close all open project and all open files. If any files have unsaved modifications, depending on the choice you made in Open Files Preferences, EditPad will ask if you want to save or not, automatically save or automatically discard the changes.
EditPad will start with a new untitled project, with one blank untitled file.
To close all files in the current project only, use Project|Close All Files, or close the project itself with Project|Close Project. To close EditPad itself, click on the X button in the upper right of the Window or select File|Exit in the menu.
File|Close All but Current
Project|Close All Files