Yes, comments like this (where the OP forgot to include the notice of decision)
https://www.canadavisa.com/canada-i...travel-document-expired.875050/#post-11104189 and this (where the OP got the rejection for missing that)
https://www.canadavisa.com/canada-i...-document-expired.875050/page-2#post-11105853
Not sure. The above is for a RTD - which is different from a work permit application.
There was no earlier step that allowed you to upload files? If there was, that was probably when you should have included these. See if you can go back.
Otherwise it might not show up until the last step. (This is the case for the online citizenship app, for example.)
Worst case, if you finish the app and never see an option - you can send a webform to attach the docs to your app. Specifically you'd use
https://secure.cic.gc.ca/ClientContact/en/Application/Form/72