code: public void addDocument(PdfReader reader, String ranges) throws DocumentException, IOException {
          fc.addDocument(reader, SequenceList.expand(ranges, reader.getNumberOfPages()));
      }
docs: Concatenates a PDF document selecting the pages to keep. The pages are described as
  ranges. The page ordering can be changed but
  no page repetitions are allowed.
  @param reader the PDF document
  @param ranges the comma separated ranges as described in {@link SequenceList}
  @throws DocumentException on error