How to add "Fix broken text" to MS Office Word 2007

I had to do this for somebody at work the other day.
Older versions of MS Office Word used to have a menu item called "Fix broken text", which would practically fix the codepage of text in the document and make special characters appear correctly in case they didn't.
Despite this function still being useful in some cases (the coworker I mentioned hasn't been the only one with this problem) it's been removed from Office 2007 and there weren't any clear instructions I could find for how to add it again. In the end I made it work and I'm going to describe how.
The following instructions might work with Office 2010 or later too, I can't say as I've not tried it.