How to get Form controls from the Process running in desktop using C# ?

Hi Everyone,

I am trying to develop the desktop plugin , to auto fill the credentials for  desktop form application (means sap, lotus note, office 365). I am trying this with C#. how to get the controls of process(means lotus note, SAP, OFFICE 356) from c#. can  I do this??

And I have already tried with GetWindowText Function to get the Window Handle. To get the controls I have used EnumChildWindow Function. I cannot get the username and password field control because all the Text And password field's Text may be Null only. so how can I get the control its by its name, can I do it ???