The 'file and contents' setting is per-extension, this is often overlooked, just FYI. I would suggest using windows for this task, as it will handle all the other bumf that composes a word document behind the scenes.
Failing that, notepad++ does an admirable job. Just Ctrl+F then find in files: http://notepad-plus-plus.org/. If we're talking docx though, you might never get any luck with plain text searches.