Catch when a form is submitted from webbrowser control...either get or post?

Question

I have a webbrowser control with a html page in it obviously. If I have a form on that page, how does c# know when that form is submitted.

If I click on a submit button within that form I want to tell c# that I clicked that button in the html. Not the other way around. I don't want to click the submit button from c#.

thanks