From the Help file
Add form fields to a form
You use the Forms toolbar to insert fields in a form that users will view and complete in Microsoft Word or in print.
In the document, click where you want to insert the form field.
Do any of the following:
Insert a fill-in field where users can enter text.
Click Text Form Field
You can specify a default entry so that the user does not have to type an entry except to change the response.
Insert a check box next to an independent option that users select or clear.
Click Check Box Form Field .
You can also use this button to insert a check box next to each item in a group of choices that are not mutually exclusive — that is, users can select more than one.
Insert a drop-down list box that restricts available choices to those you specify.
Click Drop-Down Form Field .
If needed, a user can scroll through the list to view additional choices.
Note Before you make a form available to users, protect it by clicking Protect Form on the Forms toolbar. Protection allows users to fill in the form but prevents them from changing the form's layout and its standard elements. When you want to go back to writing or modifying the form, click Protect Form again to remove protection.