I can never remember this, so I’m writing myself a note on the Internet.
Scenario: I want to reuse the same value multiple times in a Microsoft Word template document and have the fields update instantly. For example, I want to put {Customer Name} or {Date} many times in a document but only specify it once, like I would use a variable in programming.
Hack Using Document Properties
Joel, you will try for about an hour to do this on Word for Mac. You will think, “I know the button is right here.” You will Google “Microsoft Word reusable variable”, “Microsoft Word reusable fields in a document”, and “Microsoft Word insert reference”. You will get frustrated because you’ve done this many times before. It won’t work.
Open up Word for Windows. Spend a few minutes whining about “why can’t Microsoft products work the same cross platform?”
You are limited to 15 variables in your document.
Click on Insert > Quick Part > Document Property. Select one.

Turn on the Developer tab in the Ribbon. Click on Properties. You can rename this field, but the variable is tied to the document property, not the new Description attribute. Keep a reference in the name to the original property Id to keep it straight!

Finished product. After you define the variables in Word for Windows, you can populate the document in Word for Mac.
