C# is dotNet, which means that the executable-format is way different. It doesn't have anything such as exports, so you cannot use any Interop method to call it. DotNet is managed code, so you there's not a chance you can call it just like it would be native, but of course, there are workarounds. They're dirty, bad and they're called COM.
Oh, and they don't work well on Vista.
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