Use Dialog to configure the open dialog before the action fires. For example, you can set the open dialog's default extension or initially selected file at design time using the Object Inspector. From an OnAccept event handler, use Dialog to read the selected file name. 

When using a file open action, you do not place a TOpenDialog component on the form or data module at design time. Instead, you add the TFileOpen action to your action list and then use the Dialog property. The open dialog component is created by the TFileOpen constructor. 

onaccept 

oncancel 

FileName