code: public void next(PdfAction na) {
          PdfObject nextAction = get(PdfName.NEXT);
          if (nextAction == null)
              put(PdfName.NEXT, na);
          else if (nextAction.isDictionary()) {
              PdfArray array = new PdfArray(nextAction);
              array.add(na);
              put(PdfName.NEXT, array);
          }
          else {
              ((PdfArray)nextAction).add(na);
          }
      }
docs: Add a chained action.
  @param na the next action