code: public static PdfFileSpecification fileExtern(PdfWriter writer, String filePath) {
          PdfFileSpecification fs = new PdfFileSpecification();
          fs.writer = writer;
          fs.put(PdfName.F, new PdfString(filePath));
          fs.setUnicodeFileName(filePath, false);
          return fs;
      }
docs: Creates a file specification for an external file.
  @param writer the <CODE>PdfWriter</CODE>
  @param filePath the file path
  @return the file specification