code: public void addDocument(PdfReader reader, List pagesToKeep) throws DocumentException, IOException {
          fc.addDocument(reader, pagesToKeep);
      }
docs: Concatenates a PDF document selecting the pages to keep. The pages are described as a
  <CODE>List</CODE> of <CODE>Integer</CODE>. The page ordering can be changed but
  no page repetitions are allowed.
  @param reader the PDF document
  @param pagesToKeep the pages to keep
  @throws DocumentException on error