After searching quite long to find a way to call a C# Method from any JavaScript Code which is hostet in a WinForms Webbrowser Control, I found this one here:

C# Code
[ComVisible(true)]
public class ScriptManager
{
Form mForm;

public ScriptManager(Form form)
{
mForm= form;
public void MethodToCallFromScript()
{
mForm.DoSomething()
}
}
}

public class MyForm : Form
{
private Webbrowser mBrowserCtrl;

public MyForm()

{

mBrowserCtrl = new Webbrowser();
mBrowserCtrl.ObjectForScripting= new ScriptManager(this);

}

public void DoSomething(){}

}

JavaScript Code
function HandleSomething()
{
window.external.MethodToCallFromScript();
}