# File lib/ruport/formatter/pdf.rb, line 251
    def watermark(imgpath)
      x = pdf_writer.absolute_left_margin
      y = pdf_writer.absolute_bottom_margin
      width = pdf_writer.absolute_right_margin - x
      height = pdf_writer.absolute_top_margin - y

      pdf_writer.open_object do |wm|
        pdf_writer.save_state
        center_image_in_box(imgpath, :x => x, :y => y,
          :width => width, :height => height)
        pdf_writer.restore_state
        pdf_writer.close_object
        pdf_writer.add_object(wm, :all_pages)
      end
    end