PDF怎么分页啊？

 public void writeLog(string sMessage)
        {
            try
            {
                StreamWriter swriter = File.CreateText(Server.MapPath("pagetohtml.htm"));
                swriter.WriteLine(sMessage);
                swriter.Close();
            }
            catch
            { }
        }        private System.Drawing.Bitmap bitmap;
        private string url;
        private int w = 760, h = 900;        public void setBitmap()
        {
            using (WebBrowser wb = new WebBrowser())
            {
                wb.Width = w;
                wb.Height = h;
                wb.ScrollBarsEnabled = false;
                wb.Navigate(url);
                //确保页面被解析完全
                while (wb.ReadyState != WebBrowserReadyState.Complete)
                {
                    System.Windows.Forms.Application.DoEvents();
                }
                bitmap = new System.Drawing.Bitmap(w, h);
                wb.DrawToBitmap(bitmap, new System.Drawing.Rectangle(0, 0, w, h));
                wb.Dispose();
            }
        }        private void CreatPdf()
        {
            Document doc = new Document(PageSize.A4, 9, 18, 36, 36);//左右上下
            MemoryStream ms = new MemoryStream();
            try
            {
                PdfWriter writer = PdfWriter.GetInstance(doc, ms);
                writer.CloseStream = false;
                doc.Open();
                url = Server.MapPath("pagetohtml.htm");
                Thread thread = new Thread(new ThreadStart(setBitmap));
                thread.SetApartmentState(ApartmentState.STA);
                thread.Start();
                while (thread.IsAlive)
                    Thread.Sleep(100);
                bitmap.Save(Server.MapPath("pagetohtml.bmp"));                iTextSharp.text.Image img = iTextSharp.text.Image.GetInstance(bitmap, System.Drawing.Imaging.ImageFormat.Bmp);
                img.ScalePercent(75);//560 630
                doc.Add(img);
            }
            catch (Exception err)
            {
                throw new Exception(err.Message);
            }
            finally
            {
                doc.Close();
                using (FileStream fs = new FileStream(Server.MapPath("pagetohtml.pdf"), FileMode.Create))
                {
                    ms.Position = 0;
                    byte[] bit = new byte[ms.Length];
                    ms.Read(bit, 0, (int)ms.Length);
                    fs.Write(bit, 0, bit.Length);
                }
                ViewPdf(ms);
            }
        }        private void ViewPdf(Stream fs)
        {
            Response.Clear();
            //中文名的话
            //Response.AppendHeader("Content-Disposition", "attachment;filename=" +
            //             HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8) + ";charset=GB2312");
            Response.AddHeader("Content-Disposition", "attachment;FileName=pagetohtml.pdf");
            Response.AddHeader("Content-Length", fs.Length.ToString());
            Response.ContentType = "application/pdf";
            long fileLength = fs.Length;
            int size = 10240;
            byte[] readData = new byte[size];
            if (size > fileLength)
                size = Convert.ToInt32(fileLength);
            long fPos = 0;
            bool isEnd = false;
            while (!isEnd)
            {
                if ((fPos + size) >= fileLength)
                {
                    size = Convert.ToInt32(fileLength - fPos);
                    isEnd = true;
                }
                readData = new byte[size];
                fs.Position = fPos;
                fs.Read(readData, 0, size);
                Response.BinaryWrite(readData);
                Response.OutputStream.Flush();
                fPos += size;
            }
            fs.Close();
            Response.OutputStream.Close();
            Response.End();
            Response.Close();
        }