First
Document document = new Document(PageSize.A4_LANDSCAPE);
document.SetPageSize(iTextSharp.text.PageSize.A4.Rotate());Second
// it is for portrait pdf
Rectangle A4 = new RectangleReadOnly(595,842);
// For landscape
Document doc = new Document(PageSize.A4, 88f, 88f, 10f, 10f);