Use the HtmlWindow.IsClosed property to determine if the window is already closed. If the window is already closed, this method will have no effect.

When you create new windows using HtmlWindow.Open(string, string, string, bool) or HtmlWindow.OpenNew(string, string), HtmlWindow.Close causes the HTML Document Object Model to open a new instance of Internet Explorer. If you do not call HtmlWindow.Close on all of the windows you have created, this instance of Internet Explorer will remain running even after your application closes.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
Assembly Versions: 2.0.0.0