How can I search and replace in multiple Word files?

You could try VBA Find & Replace (cached link).

VBA Find and Replace© provides a method for finding and replacing text anywhere in a document (or collection of documents) using single user defined "find" and "replace" variable pairs, or a user defined list of "find" and "replace" pairs. It also provides a method to find text and replace found text with a user defined "AutoText" or "Building Block" entry.