I think I may have asked a similar question in the past, but I am still stuck...
As part of an automated process, I must \"import\" a specific subset of media files into
Mouse move/click is probably the best solution in this case. Here is something you can try. Assuming you are using windows since you put c# in the title
OR
If you are an expert of Windows you can try to do some inter process communication to send the drag and drop event to the program.