CopyText.cs

// Creating a list of File.
  List<string> file_list = new List<string>();
  //Putting Files from any Directory to this List by foreach loop.
  foreach (string file_name in Directory.GetFiles(Application.StartupPath))
      file_list.Add(file_name);
  //Clear the already copied Data of clipboard.
  Clipboard.Clear();
  //Copying File List to the Clip Board.
  Clipboard.SetData(DataFormats.FileDrop, file_list.ToArray());