Word Document in C# application

Question

Hello,

I have a web application that opens a Word Document from the code
what I need to do next is : when the user closes the window ( not important if he does save first)   a messagebox should appear asking if he is approving the document or not ( different from Changes have been made, would u like to save them? message)

any ideas how I do this?

Thank you  for any help
Probi