The procedure described above is the way to do it, BUT there are some PDF forms that are created in a way to allow text insertion just by clicking on the box or space. Apparently the one kevs is working with is not one of those types and the somewhat tedious method joemikeb lays out is the way to go in Preview.

On a Mac since 1984.
Currently: 24" M1 iMac, M2 Pro Mac mini with 27" BenQ monitor, M2 Macbook Air, MacOS 14.x; iPhones, iPods (yes, still) and iPads.