Microsoft Windows 8/10 uses own .deskthemepack file format to store customized Windows themes, but it can also use .themepack files from Windows 7.
Simply double click on .themepack file and Windows 8/10 will use Windows 7 theme. If you want to create .deskthemepack file → save current theme in Control Panel - Individual Settings. The themepack to deskthemepack conversion will be done automatically.