To hide the mini toolbar permanently, click the Office button in the top left corner of the window. Select "Word Options" in the window that opens and then look at the "Popular" section from the categories on the left.

Then uncheck the checkbox in front of the "Show Mini Toolbar on selection" option. Confirm the modification with "OK". The formatting commands from the now missing mini tool bar can still be accessed from their regular positions on the" Home" tab of the multi-function bar.