code: public ArrayList getBlankSignatureNames() {
          getSignatureNames();
          ArrayList sigs = new ArrayList();
          for (Iterator it = fields.entrySet().iterator(); it.hasNext();) {
              Map.Entry entry = (Map.Entry)it.next();
              Item item = (Item)entry.getValue();
              PdfDictionary merged = item.getMerged(0);
              if (!PdfName.SIG.equals(merged.getAsName(PdfName.FT)))
                  continue;
              if (sigNames.containsKey(entry.getKey()))
                  continue;
              sigs.add(entry.getKey());
          }
          return sigs;
      }
docs: Gets the field names that have blank signatures.
  
  @return the field names that have blank signatures