using (FileStream fs = new FileStream(pdf, FileMode.Open))
                {
                    MemoryStream ms=new MemoryStream();
                    fs.CopyTo(ms);
                    Response.Clear();
                    Response.ContentType = "application/pdf";
                    Response.AddHeader("content-length", ms.Length.ToString());
                    Response.BinaryWrite(ms.ToArray());
                    Response.Flush();
                    ms.Close();
                    File.Delete(pdf);
                }