To better define your question:
If someone clicks in the Institution box you want to activate a drop-down? (or)
If someone clicks in the Institution box you want the choices to all appear as a part of the document?

Are your fields legacy form fields (those designed for protected documents) or the new content control fields?

I am assuming you have macros enabled.
Assuming these are legacy form fields, the field with your drop-down needs to have a name set in the properties to use in your macro.