If you are the applicant of the DA and it was lodged via the Planning Portal, you can access all your documents via the NSW Planning Portal.
If you engaged a third party (Private Certifier/Architect/Planning Consultant etc) to process your DA or other applications, you can liaise with them to provide all the documents.
You can access the Notice of Determinations (Consent/Approval or Refused) for Development Applications (DAs) and Modification DAs via the DA Tracker.