If you want another device to access a course file, you need to:
a) provide the full URL to the file (e.g. http://www.yourLMS.com/courses/1234/files/mydoc.pdf)
b) make sure that the URL is accessible (99% of LMS will block unauthenticated users from accessing course files)
So I’d suggest uploading the document somewhere, where it would be accessible for anyone (your website, dropbox, google drive, your LMS might have a special place etc).
Once you solve the access problem, generate QR code from URL using one of hundreds online services, paste the picture into your course and voila.
Finally, don’t forget that there are best practices of using QR codes, e.g. you should always provide a short URL (goo.gl is great) next to the QR code for those users who cannot scan it. Relying on QR codes alone is risky, because lots of users will not have the reader app installed, won’t be able to scan it, etc etc, so always provide an alternative way of accessing the file.