If you do not want users to change the contents of a control, you can make the control read-only.
Note: This option is available only for text boxes, rich text boxes, bulleted lists, numbered lists, and plain lists.
Right-click the control that you want to set as read-only, and then click Control Properties on the shortcut menu.
Click the Display tab.
Select the Read-only check box.
Note: Making a control read-only prevents users from typing in that control, but it does not affect the control's appearance in any way.
Tip: You can also use conditional formatting to make a control read-only unless a specific value is entered into another control. For example, a text box for a driver's license number can be read-only unless the user enters an appropriate age into another control on the form.