string imagePath = "http://zzazz.org/wp-content/uploads/2018/08/trend-micro-deep-security-logo-300x150.png";
    iTextSharp.text.Image img = iTextSharp.text.Image.GetInstance(imagePath);
    img.Alignment = Element.ALIGN_CENTER; //sprawdz czy jest np ALIGN_RIGHT
    img.ScaleToFit(180f, 250f);

    pdfdoc.Add(image);