It's hard to remember for sure - I'm either too old or I slept through that part of the class

- but I think I learned the same thing. That is, the passive voice is okay as long as you don't overuse it - so for some writing teachers, that sort of meant "don't use it."
And I'm with the others - I look at Word's suggestion(s) and decide if I like MY version better than its version... and if I like my way better, I leave it that way. And ignore Word's whining about it.
~Toc