Here is the code. You can also used Application.StartupPath.
Also, your subject is slightly wrong as you say Asp.Net Windows Application as the ASP.Net is used for Web based app only.
var path = System.IO.Directory.GetCurrentDirectory();
var files = Directory.GetFiles(path).Select(f=>Path.GetFileName(f)).ToList();
files.ForEach(f => Console.WriteLine(f));
Console.ReadKey();