In May 2019, D2L is ending support for it’s Binder mobile app. The app will no longer be available in iOS and Android stores, and D2L will supply no more updates to it to match changes to those mobile operating systems. If you have the app installed, and use it to store and annotate files from your D2L courses, it might work for some time after May but you should plan to replace it with another app.
Since D2L is now mobile responsive, you can do many of the same things in your mobile device’s browser as you do on the desktop. This means downloading course files, such as .docx or .pdf, is easy to do. Take advantage of excellent apps for iOS and Android that provide management and annotation options for these files.