The following code working fine for me.
iTextSharp.text.Document document = new iTextSharp.text.Document(new Rectangle(288f, 144f), 10, 10, 10, 10);
document.SetPageSize(iTextSharp.text.PageSize.A4);
PdfWriter writer = PdfWriter.GetInstance(document, new FileStream(filename, FileMode.Create));
iTextSharp.text.Font font5 = iTextSharp.text.FontFactory.GetFont(FontFactory.HELVETICA, 10);
document.Open();
PdfPTable table = new PdfPTable(MainTable.Columns.Count);
PdfPRow row = null;
float[] widths = new float[] { 5f, 4f };
table.SetWidths(widths);
table.WidthPercentage = 100;
iTextSharp.text.Image logo = iTextSharp.text.Image.GetInstance(Server.MapPath("IMAGE URL"));
PdfPCell cell1 = new PdfPCell(logo);
cell1.Colspan = MainTable.Columns.Count;
cell1.Padding = 5;
table.AddCell(cell1);
document.Add(table);
Paragraph footer = new Paragraph("Your Company Name", FontFactory.GetFont(FontFactory.TIMES, 10, iTextSharp.text.Font.NORMAL));
footer.Alignment = Element.ALIGN_RIGHT;
PdfPTable footerTbl = new PdfPTable(1);
footerTbl.TotalWidth = 500;
footerTbl.HorizontalAlignment = Element.ALIGN_CENTER;
PdfPCell cell2 = new PdfPCell(footer);
cell2.Border = 0;
cell2.PaddingLeft = 0;
footerTbl.AddCell(cell2);
footerTbl.WriteSelectedRows(0, -1, 550, 30, writer.DirectContent);
document.Close();