Aspose.Word does not automatically update fields on document open. You need to call Document.Range.UpdateFields if you want to update the fields, but at the moment it updates the results of DOCPROPERTY and DOCVARIABLE fields only. See the API reference http://www.aspose.com/Products/Aspose.Word/Api/Aspose.Word.Range.UpdateFields.html
We will implement update of other fields in the future.
However, I don't quite understand what sort of update you want for the CREATEDATE field as it is supposed to return the date the document was created and this date does not really change.
Ah, by the way, for your case there is a workaround, use the DOCVARIABLE field to insert the create date/time. In MS Word select Insert/Field, select DocVariable and select CreateTime.