创建pdf错误消息(..文件已损坏，无法修复)

我创建了一个pdf文件并发送了一封电子邮件。邮件发送的很好，但是要打开pdf，我一直得到以下错误:"打开此文档出错。文件已损坏，无法修复"。这是代码。我不确定我做错了什么……

       Document myDoc = new Document(PageSize.LETTER, 20f, 20f, 18f, 20f);
        using (MemoryStream ms = new MemoryStream())
        {
            PdfWriter pWriter = PdfWriter.GetInstance(myDoc, ms);
            myDoc.Open();
            PdfPTable table = new PdfPTable(2);
            table.WidthPercentage = 100;
            table.SpacingAfter = 10;
            float[] widths = new float[] { 1f, 2f };
            table.SetWidths(widths);
            table.HorizontalAlignment = 0;
            table.SpacingBefore = 20f;
            table.SpacingAfter = 30f;
            Font regularFont = new Font(iTextSharp.text.Font.FontFamily.HELVETICA, 12);
            Font boldFont = new Font(iTextSharp.text.Font.FontFamily.HELVETICA, 14, 1);
            Font headerFont = new Font(iTextSharp.text.Font.FontFamily.HELVETICA, 18, 1);
            PdfPCell cell = new PdfPCell();
            cell.BorderWidth = 1;
            cell = new PdfPCell(new Phrase("HEADER", headerFont));
            cell.Colspan = 2;
            cell.HorizontalAlignment = 1; 
            table.AddCell(cell);
            cell.Colspan = 1;
            cell.HorizontalAlignment = 0; 
            cell.Phrase = new Phrase("CONTENT:", boldFont);
            table.AddCell(cell);
            cell.Phrase = new Phrase("content", regularFont);
            table.AddCell(cell);
            myDoc.Add(table);
            MailMessage msg = new MailMessage();
            msg.From = new MailAddress("store@email.com", "CONTENT Report");
            msg.To.Add(new MailAddress("user@email.com"));
            msg.Subject += "Content Report";
            msg.Body += "Message.<br> :)";
            msg.IsBodyHtml = true;
            ms.Position = 0;
            msg.Attachments.Add(new Attachment(ms, "test.pdf", "application/x-pdf"));
            SmtpClient client = new SmtpClient("10.1.1.15");
            client.Send(msg);

 myDoc.Close();