when I try to download I get error messages.... Microsoft office cannot open this file because some parts are missing or
invalid.

You'll need to be a bit more specific to get a coherent solution to your problem.
A) Which font are you having problems with?
B) have you read the FAQs here:
http://www.dafont.com/faq.php
regarding installing the font correctly?
If you are trying to open a downloaded font with Office as far as I'm aware you will get errors. Install it according to the instructions on the FAQs and that should sort you out.

It could have this worked out by itself pilaster. That is, if it had ever taken the trouble to try to understand what it is doing