using (MemoryStream ms = new MemoryStream())
        {
            doc.SaveAs(ms);

            Response.Clear();
            Response.AddHeader("Content-Disposition", string.Format("attachment; filename={0}", fileName));
            Response.ContentType = "application/vnd.openxmlformats-officedocument.wordprocessingml.document";
            ms.WriteTo(Response.OutputStream);
            Response.End();
        }