code: public float getDescender() {
          float descender = 0;
          for (int k = 0; k < line.size(); ++k) {
              PdfChunk ck = (PdfChunk)line.get(k);
              if (ck.isImage())
                  descender = Math.min(descender, ck.getImageOffsetY());
              else {
                  PdfFont font = ck.font();
                  descender = Math.min(descender, font.getFont().getFontDescriptor(BaseFont.DESCENT, font.size()));
              }
          }
          return descender;
      }
docs: Gets the biggest descender for all the fonts used
  in this line.  Note that this is a negative number.
  @return maximum size of all the ascenders used in this line