How to Toggle Field Codes in Microsoft Word
After you insert a Merge field into a Microsoft Word Document, you will see the name of the field ("Last Name" for example)
If you want to see the Field code associated with that field, right-click the field and select Toggle Field Codes
You will then see something similar to the following:
If you want to toggle field codes for all your merge fields, press Alt-F9 on your keyboard.
This will reveal the codes for all merge fields in your document.