protected void btnExport_Click(object sender, EventArgs e)
    {
        string mimeType, encoding, fileNameExtension;
        Warning[] warnings;
        string[] streams;

        var sb = new StringBuilder(1024);
        var xr = XmlWriter.Create(sb);
        xr.WriteStartElement("DeviceInfo");
        xr.WriteElementString("DpiX", "300");
        xr.WriteElementString("DpiY", "300");
        xr.Close();

        byte[] bytes = ReportViewer1.ServerReport.Render("PDF", sb.ToString(), out mimeType, out encoding,
                                            out fileNameExtension, out streams, out warnings);

        Response.ContentType = "application/pdf";
        Response.AppendHeader("Content-Disposition", "attachment; filename=Test.pdf");
        Response.BinaryWrite(bytes);
    }