Not sure if anyone from Microsoft looks at this but this would be a welcome addition to the Cloud Assignment feature.
1. Upload a PDF to the Cloud Assignment
2. Open the Assignment in Edge (which has PDF editing functionality though the stylus/hand)
3. Submit assignment with annotations in place!
Certainly would fulfil plenty of requirements and offer more functionality to the integration.
I notice that Kami now have an integration with Google Docs that allows this - Using Kami's Canvas Integration [UPGRADED] | Kami Help Center