Yeah, that is what my understanding was with PR application we usually get the file number. Now if I read the email correctly I do not have the file number, however I am able to login to https://cst-ssc.apps.cic.gc.ca/en/login with the UCI and status says in progress which is kind of confusing me.We use several terms and acronyms here I guess. Usually the emails were generally worded with "acknowledgement" in them.
Essentially AOR means that they are letting you know that they received your application, it is complete, they have created a file for you in their system, and it is in progress. And you can use the File/Application number to track it online using the tracker.