Is it safe to allow an apple store to do this when trading in?

Hello Notanotherscreen,

Thanks for using the Apple Support Communities. We understand you have questions on preparing your old device for trade in with Apple. As long as you follow the article linked to your post, What to do before you sell, give away, or trade in your Mac, there shouldn't be no concern regarding anything being able to access data that was stored on your Mac.

As for Microsoft office, you'll need to download the application, and may need to sign into your Microsoft Office account or provide the product key that was supplied when you purchased the application. If you have any questions regarding that process, connecting with Microsoft Support would be your best option.

Best regards.