code: public void setSortOrder(boolean ascending) {
  		PdfObject o = get(PdfName.S);
  		if (o instanceof PdfName) {
  			put(PdfName.A, new PdfBoolean(ascending));
  		}
  		else {
  			throw new IllegalArgumentException("You have to define a boolean array for this collection sort dictionary.");
  		}
  	}
docs: Defines the sort order of the field (ascending or descending).
  @param ascending	true is the default, use false for descending order