Using InstanceCookie (note that if you have an entire folder of .instance files, there's a more efficient way to get all of them):

 DataObject dob = DataObject.find (theDotInstanceFileObject);
InstanceCookie ck = (InstanceCookie) dob.getCookie (InstanceCookie.class);
MyObject obj = (MyObject) ck.instanceCreate();

Source: NetBeans FAQ