OpenFileDialog

Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog();
  dlg.FileName = "Document"; // Default file name
  
  dlg.DefaultExt = ".txt"; // Default file extension
  
  dlg.Filter = "Text documents (.txt)|*.txt"; // Filter files by extension
  
  
  // Show open file dialog box
  
  Nullable<bool> result = dlg.ShowDialog();
  
  // Process open file dialog box results
  
  if (result == true)
  {
      // Open document
  
      string filename = dlg.FileName;
  }