I'm writing a dll for an aging software framework. The framework was created in 2002, so most of its thinking and dll templates are for C++/Win32. However, it does come with a working dll template in C#, which is what I'm working with. The dll creates a window and I'm trying to add a tooltip to that window. Using the C++/Win32 dll templates, I can add a tooltip using Win32 functions like CreateWindowEx, SendMessage, etc. But I can't figure out how to add a tooltip in the C# template. The dll gives me a Win32-type handle to the window in question, but .Net tooltips work with .Net forms, not Win32 handles. Is there a way to use the Win32 window handle in .Net context, so that I can create a .Net tooltip for that window?