Open a Finder window, navigate to the root folder (the top-most folder that contains the sub- and sub-sub- folders) and type .docx into the search bar in the top right of the Finder window and it will show all of the .docx files contained in the folder and all of its sub-folders, all of their sub-folders, etc.
If you have to find .docx and .doc files, you can either do this twice or “level up” and click into the search bar in the top right of the Finder window, hit the space bar, and then click the plus sign that pops up below that search bar which gives you a “smart search” (like a Smart Folder) that you can do a lot with.
The default is to search by Name but to achieve what you want to you have to hold the Option key down and then click the “…” on the right side of the finder window which opens an “Any of the following are true” search parameter that should look like this:
From there, click the plus sign to the right of the first search parameter that is inside the “Any” parameter so that there are two, and then set their initial parameters to “File extension”, which may or may not be in the short dropdown list. If they aren’t, click “Other…” at the bottom and find them in the window that pops up there, then set the extensions to .doc and .docx
Now you will have something that looks like this:
Which should show you exactly what you want!