How to download file with open/save dialog box in ASP.Net?

if (File.Exists(strDestinationPath))
  {
    byte[] file = File.ReadAllBytes(strDestinationPath);

    // Create a memory stream from those bytes.
    using (MemoryStream memory = new MemoryStream(file))
        {
          Response.Clear();
          Response.ContentType = "application/octet-stream";
          Response.AddHeader("Content-Disposition", "attachment; filename=" + Path.GetFileName(strDestinationPath));
          Response.AppendHeader("content-length", file.Length.ToString());
          Response.BinaryWrite(memory.ToArray());
          Response.Flush();
          Response.Close();
          //Response.End();
        }
  }
else
  {
    ShowPopupAlert("File Does not Exists");
    return;
  }