The method updates PDF’s XMP metadata.
Note, that date may appear in PDF in two different formats.
XMP metadata: “2009-11-27T18:25:45+01:00”
PDF info object: “D:20091127182545+01’00′”
So you’ll probably also need to call
pd4ml.setParam(Constants.PD4ML_DOCUMENT_DATE, "D:20091127211216+01'00'"); to keep the doc dates in sync