Hello wbarnardGTEV5, apologies for the delay in replying.
The search bar in the Office plugins only searches Documents (non-CAD files). Further, after a bit of testing, it seems it only searches documents found in the Documents section of projects, not any documents attached to items. See the images below.

If you would like to see some expanded functionality in this search bar, then please submit your ideas to the Upchain Ideas Board. If your plugin is not returning any results when you believe it should, please upgrade your plugin to the latest version. If it still isn't working, please submit a support request.
For some further resources on the Office plugins, this Upchain Academy course goes into the Office plugins in more detail. This series of help topics go through the Office plugin functionality.
Hope that all helps! 🙂