A family of Microsoft word processing software products for creating web, email, and print documents.
Re: "...doesn't Word already, out of the box, use Command-F?"
Prior to Office 2011, yes. My understanding is that Microsoft was 'persuaded' to concede that keystroke in order to comply with Apple's User Interface Guide which assigns Command+F to the OS X Find [aka, Search in Document] command. As I wrote, Apple has been confiscating keyboard combinations since the introduction of OS X 10.7 (Lion). Along with that, the Word feature formerly know as Find was re-dubbed Advanced Find & Replace [EditAdvancedFind] but no built-in keystroke was created for it.
I believe Command+F can be reassigned to EditAdvancedFind in 10.6.x but I'm not sure about later versions of OS X.
Another way to look at it is that Command+F still executes the Find command but the feature it calls is Apple's contrivance, not Word's long-standing traditional assignment.