Catch the close event in word and Powerpoint for Override in Office Add-ins

Question

Please can anyone tell me how to catch the closing event ( [X] button of my window) I need to kill all the threads running when someone would press [X] button in MS WORD and POWER POINT. I am Creating some Office plug ins by using Addins in C#. And

Please can anyone tell me How to disable the default messages like (Do you want to save the document ) in word and power point when document is going to close.