Hi Melanie,
Are your students using any of the Canvas mobile apps? If they are, they they can annotate PDF on their tablet devices and then send that PDF to another drive or even submit it in Canvas.
How do I submit a PDF assignment with annotations in the Student app on my iOS device?
How do I submit a PDF assignment with annotations in the Student app on my Android device?
I just tried it from my Android phone:

The caveat with mobile device is that the PDF markup & submit works best for 1:1. If multiple students are sharing the same device there's uncertainty of which PDF belongs to which student especially if everyone has downloaded the same document.
Otherwise, you may have to look at options for annotating in the browser with Edge or Chrome.
Let us know what you end up doing,
Cheers - Shar 
This discussion post is outdated and has been archived. Please use the Community question forums and official documentation for the most current and accurate information.