code: public void addFileAttachment(String description, byte fileStore[], String file, String fileDisplay) throws IOException {
          addFileAttachment(description, PdfFileSpecification.fileEmbedded(stamper, file, fileDisplay, fileStore));
      }
docs: Adds a file attachment at the document level. Existing attachments will be kept.
  @param description the file description
  @param fileStore an array with the file. If it's <CODE>null</CODE>
  the file will be read from the disk
  @param file the path to the file. It will only be used if
  <CODE>fileStore</CODE> is not <CODE>null</CODE>
  @param fileDisplay the actual file name stored in the pdf
  @throws IOException on error