Sets a new Mainframe for API offline program. API offline program will show all dialogs which are normally hidden in add-ins. It is possible to hide such dialogs using ResetQuietMode method.
p.e. form1 is a System.Windows.Forms.Form
Eplan.EplApi.System.EplApplication app = new Eplan.EplApi.System.EplApplication();
app.SetMainFrame(form1.Handle);