I need to access the handle of the window for a dll ...

Hello, Been some time sense I have been on here last… Anyway, I have a way to play MIDI files on unity… I use a .dll… This dll requires a window handle though… How do I access the editor window handle or the executable handle? or if need be, create a new window form? I know I need to use using system.windows.forms but unity throws an error.
also The dllimport thing looks kinda like this.

[Dllimport("midi.dll",CallingConvention= Callingconvention.cdecl)
public static extern double midi_init_ext(Double windowHandle, Double Device);

This is a very easy approach in C# alone but It is causing me a problem in unity…
Thanks to all in advance

What happens if you pass in a null for the window handle?
The ‘Double’ types btw seem a crude way to pass 64-bit pointers.