I couldnt extract the contents of that sample.zip file... however I think the sample project and corresponding code is actually an Excel Sheet with builtin Macros or VBA code. So... I dont think you can actually open it using Visual Studio, more like try using the Macro Editor or VBA design mode within Excel.

For your question about the dropdown box, see if you can find out where the dropdown box is supposed to retrieve information from ie sheet1, cell A2 etc and see if there is any data there.