Create PDF In Memory Instead Of Physical File

using iTextSharp.text;
using iTextSharp.text.pdf;

public ActionResult ExportPDF() {
    PdfPTable fieldServiceReportDesign = MainPage();
    Document document = new Document(PageSize.A4, 0 f, 0 f, 0 f, 17 f);
    MemoryStream stream = new MemoryStream();
    using(PdfWriter pdfWriter = PdfWriter.GetInstance(document, stream)) {
        pdfWriter.CloseStream = false;
        document.Open();
        document.Add(fieldServiceReportDesign);
        document.Close();
        stream.Flush(); //Always catches me out
        stream.Position = 0;
    }
    return File(stream, "application/vnd.pdf", "PDF_" + DateTime.Now.Ticks + ".pdf");
}
private PdfPTable MainPage() {
    //Main table
    PdfPTable table = new PdfPTable(1);
    table.WidthPercentage = 100;
    table.DefaultCell.BackgroundColor = new BaseColor(255, 255, 255);
    table.HorizontalAlignment = Element.ALIGN_CENTER;
    table.HeaderRows = 2;
  #region Header
    //header details
    PdfPHeaderCell hcell = new PdfPHeaderCell();
    hcell.Border = 0;
    hcell.Padding = 7 f;
    hcell.BackgroundColor = new BaseColor(5, 150, 215);
    hcell.HorizontalAlignment = Element.ALIGN_CENTER;
    hcell.AddElement(GetHeader("PDF"));
    table.AddCell(hcell);
    //space
    hcell = new PdfPHeaderCell();
    hcell.Border = 0;
    hcell.Padding = 7 f;
    hcell.MinimumHeight = 10 F;
    hcell.BackgroundColor = new BaseColor(255, 255, 255);
    hcell.HorizontalAlignment = Element.ALIGN_MIDDLE;
    table.AddCell(hcell);
  #endregion
    PdfPCell cell = new PdfPCell();
    hcell.Border = 0;
    hcell.Padding = 7 f;
    hcell.MinimumHeight = 10 F;
    hcell.BackgroundColor = new BaseColor(255, 255, 255);
    hcell.HorizontalAlignment = Element.ALIGN_MIDDLE;
    hcell.AddElement(GetData());
    table.AddCell(hcell);
    //leave blank
    cell = new PdfPCell();
    cell.Border = 0;
    cell.Padding = 0;
    cell.BackgroundColor = new BaseColor(255, 255, 255);
    cell.HorizontalAlignment = Element.ALIGN_MIDDLE;
    table.AddCell(cell);
    table.SplitLate = false;
    return table;
}
private PdfPTable GetHeader(string headerText) {
    PdfPCell cell = null;
    Phrase phrs = null;
    //Header design table
    PdfPTable table = new PdfPTable(1);
    table.WidthPercentage = 100;
    table.DefaultCell.Padding = 0;
    table.DefaultCell.Border = 0;
    table.HorizontalAlignment = Element.ALIGN_CENTER;
    phrs = new Phrase();
    phrs.Add(new Chunk(headerText, new iTextSharp.text.Font(iTextSharp.text.Font.FontFamily.HELVETICA, 11 f, iTextSharp.text.Font.BOLD, new BaseColor(255, 255, 255))));
    cell = new PdfPCell(phrs);
    cell.Border = 0;
    cell.HorizontalAlignment = Element.ALIGN_CENTER;
    cell.VerticalAlignment = Element.ALIGN_MIDDLE;
    table.AddCell(cell);
    return table;
}
private PdfPTable GetData() {
    PdfPCell cell = null;
    Phrase phrs = null;
    //body design table
    PdfPTable table = new PdfPTable(1);
    table.WidthPercentage = 100;
    table.DefaultCell.Padding = 0;
    table.DefaultCell.Border = 0;
    table.HorizontalAlignment = Element.ALIGN_CENTER;
    phrs = new Phrase();
    phrs.Add(new Chunk("Hello !", new iTextSharp.text.Font(iTextSharp.text.Font.FontFamily.HELVETICA, 10 f, iTextSharp.text.Font.NORMAL, new BaseColor(0, 0, 0))));
    cell = new PdfPCell(phrs);
    cell.Border = 0;
    cell.HorizontalAlignment = Element.ALIGN_CENTER;
    cell.VerticalAlignment = Element.ALIGN_MIDDLE;
    table.AddCell(cell);
    return table;
}