code: public void setFields(FdfReader fdf) throws IOException, DocumentException {
          HashMap fd = fdf.getFields();
          for (Iterator i = fd.keySet().iterator(); i.hasNext();) {
              String f = (String)i.next();
              String v = fdf.getFieldValue(f);
              if (v != null)
                  setField(f, v);
          }
      }
docs: Sets the fields by FDF merging.
  
  @param fdf the FDF form
  @throws IOException on error
  @throws DocumentException on error