Are you pasting content from Word into the visual editor? If so, and you are using the default visual editor with WordPress, there is a button that allows you to paste from Word. By default, the button is not shown. If you look at the top row of buttons above the editor, the icon on the far right, when you hover over it, says something like “kitchen sink”. If you click that button, another row of buttons will appear. There is a button that has a “W” on it, this is the paste from word button. If you use this when pasting from word, it will clean off all of the word tags.
I think that would be much easier than figuring out how to get that command blocked in the php. ??