code: public static PdfFileSpecification url(PdfWriter writer, String url) {
          PdfFileSpecification fs = new PdfFileSpecification();
          fs.writer = writer;
          fs.put(PdfName.FS, PdfName.URL);
          fs.put(PdfName.F, new PdfString(url));
          return fs;
      }
docs: Creates a file specification of type URL.
  @param writer the <CODE>PdfWriter</CODE>
  @param url the URL
  @return the file specification