public void SetCreatorInfo(String creator, String subtype)
{
PdfDictionary usage = Usage;
PdfDictionary dic = new PdfDictionary();
dic.Put(PdfName.CREATOR, new PdfString(creator, PdfObject.TEXT_UNICODE));
dic.Put(PdfName.SUBTYPE, new PdfName(subtype));
usage.Put(PdfName.CREATORINFO, dic);
}