code: public void setCreatorInfo(String creator, String subtype) {
          PdfDictionary usage = getUsage();
          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);
      }
docs: Used by the creating application to store application-specific
  data associated with this optional content group.
  @param creator a text string specifying the application that created the group
  @param subtype a string defining the type of content controlled by the group. Suggested
  values include but are not limited to <B>Artwork</B>, for graphic-design or publishing
  applications, and <B>Technical</B>, for technical designs such as building plans or
  schematics