Ran into a problem today where users were trying to download Office 2007
documents from a web site, but were prompted to save them as a Zip file.
Turns out the new extensions for Office 2007 documents (docx, xlsx,
pptx, etc) need to be added with a new mime-type for Apache to serve
them up correctly.

It’s a pretty simple fix.

In /etc/mime.types add this:

application/vnd.openxmlformats docx pptx xlsx

Save and restart Apache, then the documents should be handled correctly.