There are several ways of viewing Microsoft Office documents that mean that as a teacher, you can be confident that you and your students can always access your resources.
Option 1 (recommended)
When the document is visible via the Office Viewer, it's displayed directly in the browser - no need to download the file at all. Choose the fullscreen option to see the whole document. The types of documents that can be viewed in this way are: Word, Excel, Powerpoint, PDF.
To download the file, choose Download a Copy from the Office Viewer options.
If the document appears as part of a file list, then clicking on the link will give you the option to open the file in the associated Office application. By cancelling any further popup screens that may appear, the file will download in the expected way.