I apologize for the confusion. Microsoft has confounded all of us by naming different features/controls the same and using the term "Form" to mean all sorts of different things. It is confusing for all of us.
I would use mapped content controls for your ComboBoxes. See:
Then test a copy of your mapped ComboBox in an
IF Field for the condition you want to result in display of your text. Note that IF fields are case-sensitive. Use an AutoText field as your truetext result in the IF field.
The AutoText should be stored in your
document template. If the document will be separated from the template, you can lock or unlink that field upon completion of your form.
The reason for using mapped controls is it saves having to bookmark the controls and use a REF fields in your IF field. Also, mapped controls update instantly which is not true of REF fields.
Note that Paul knows far more about fields than just about anyone else. There are several of his tutorials on them pinned to the start of this forum.