Good evening, @LouWalder ...
The way that I have heard others do what you are wanting is to use something like Google Drive or Microsoft OneDrive to store those files. Then, you would use the harvested embed code from those services to add the documents to your courses in Canvas. In this way, if you make a change to the document in Google Drive or OneDrive, it should update the content everywhere it is linked. Obviously, you'd want to do some testing on this to make it sure that it is working the way you want. You might want to check with your school's IT department to see if they use either Google or Microsoft ... as they may have a preferred way for you to store your files outside of Canvas.
Hope this helps a bit. Sing out if you have any other questions about this...thanks!