ASP.NET - Problemas de tabulacion de datos con ItextSharp

public void SetPdf()

        {

            PdfPTable PdfTable = new PdfPTable(GridView2.HeaderRow.Cells.Count);

            //BaseFont bfTimes = BaseFont.CreateFont("c:/windows/fonts/arial.ttf", BaseFont.IDENTITY_H, BaseFont.EMBEDDED);

            //iTextSharp.text.Font _standardFont = new iTextSharp.text.Font(iTextSharp.text.Font.FontFamily.HELVETICA, 8, iTextSharp.text.Font.NORMAL, BaseColor.BLACK);

            BaseFont bfTimes = BaseFont.CreateFont("c:/windows/fonts/arial.ttf", BaseFont.IDENTITY_H, BaseFont.NOT_EMBEDDED);

            Font fuente = new Font(bfTimes, 7);

            foreach (GridViewRow gridViewRow in GridView2.Rows)

            {

                foreach (TableCell tableCell in gridViewRow.Cells)

                {

                    String texto = HttpUtility.HtmlDecode(tableCell.Text);

                    Phrase p = new Phrase(texto, fuente);

                    p.Add(new VerticalPositionMark());

                    PdfPCell pdfCell = new PdfPCell(p);

                    pdfCell.BorderWidthBottom = 0f;

                    pdfCell.BorderWidthLeft = 0f;

                    pdfCell.BorderWidthTop = 0f;

                    pdfCell.BorderWidthRight = 0f;

                    PdfTable.AddCell(pdfCell);

                }

            }

            Session["pdf"] = PdfTable;

        }

public partial class VisorPdf : System.Web.UI.Page

    {

        protected void Page_Load(object sender, EventArgs e)

        {

            PdfPTable pdf = (PdfPTable)Session["pdf"];

            String archivo = Request.QueryString["filename"];

            Response.ContentType = "application/pdf";

            Response.AddHeader("content-disposition", string.Format("inline;filename=" + archivo));

            Document pdfDocument = new Document(PageSize.LETTER);

            PdfWriter.GetInstance(pdfDocument, Response.OutputStream);

            pdfDocument.Open();

            pdfDocument.Add(pdf);

            pdfDocument.Close();

            Response.End();

        }

    }

Document pdfDocument = new Document(PageSize.A4, 0f, 0f, 0f, 0f);

pdfDocument.Open();

            pdfDocument.SetMargins(10f, 0f, 0f, 0f);

            pdfDocument.NewPage();

            pdfDocument.Add(PdfTable);

            pdfDocument.Close();