code: public void setGenerateAppearances(boolean generateAppearances) {
          this.generateAppearances = generateAppearances;
          PdfDictionary top = reader.getCatalog().getAsDict(PdfName.ACROFORM);
          if (generateAppearances)
              top.remove(PdfName.NEEDAPPEARANCES);
          else
              top.put(PdfName.NEEDAPPEARANCES, PdfBoolean.PDFTRUE);
      }
docs: Sets the option to generate appearances. Not generating appearances
  will speed-up form filling but the results can be
  unexpected in Acrobat. Don't use it unless your environment is well
  controlled. The default is <CODE>true</CODE>.
  
  @param generateAppearances the option to generate appearances