code: protected PdfDictionary mergeAttrib(PdfDictionary parent, PdfDictionary child) {
          PdfDictionary targ = new PdfDictionary();
          if (parent != null) targ.putAll(parent);
          
          for (Iterator it = child.getKeys().iterator(); it.hasNext();) {
              PdfName key = (PdfName) it.next();
              if (key.equals(PdfName.DR) || key.equals(PdfName.DA) ||
              key.equals(PdfName.Q)  || key.equals(PdfName.FF) ||
              key.equals(PdfName.DV) || key.equals(PdfName.V)
              || key.equals(PdfName.FT)
              || key.equals(PdfName.F)) {
                  targ.put(key,child.get(key));
              }
          }
          return targ;
      }
docs: merge field attributes from two dictionaries
  @param parent one dictionary
  @param child the other dictionary
  @return a merged dictionary