Double clicking on a filename in the UltimateZip window will perform the same action performed when you double click on a file in the Explorer or the Windows Desktop. If the file has an executable extension like EXE, COM or BAT, UltimateZip will run it. Otherwise, UltimateZip will open the file with the associate program. For example, files with the extension of .BMP are opened by Paint (unless you have changed the .BMP association).