Microsoft Office 365 for the Mac seems to have a bug that prevents activation in El Capitan and Yosemite. Here's the fix.
How to activate Microsoft Office 365 when stuck on “Loading”
How to Show (and Hide) Invisible Characters like Paragraph Marks in Microsoft Word on a Mac
Light blue marks in your Word documents are "invisible characters" (returns, tabs, & spaces). Here's how to turn them off, and back on.