Common interface between all office applications

[Jimmy Badawy]

I am writing an office addin in C#. Is there a common interface that
Word.Application and Excel.Application both implement.
currently i am doing the following

public void OnConnection(object application, Extensibility.ext_ConnectMode
connectMode, object addInInst, ref System.Array custom)
{
try
{
appObject = (Word.Application)application;
}
catch(Exception t)
{
System.Windows.Forms.MessageBox.Show(t.ToString());
}
}

I need the type of appObject to be this interface if it exists.
I saw some exaples using envDte._DTE, I tried it and it didn't work
Can anyone help.