Is it possible to add files to one course and make them accessible from other courses?
Not necessarily in the way one might expect — it really depends on how you're envisioning this might work or the particulars of your use case / requirements. Taking a literal interpretation of your question, however, there is no way to add files to a course offering and have them automatically push/appear in related course offerings.
However, you can accomplish something similar by either
This article does a great job mapping out / comparing some of the tools you may want to use (along with some important considerations): Deciding Between Using Manage Files, Public Files, or LOR
I hope that helps get you stared in the right direction!
Learning Administration Manager
Thanks Jeffrey. I'll give these a try.