You can specify what fields are validated by a signature field. To configure a signature field:
After inserting the signature field the from the Toolbox window, select the signature field.
In the Properties pane, click the edit button next to Configure Signed Fields. The Signed Fields screen is displayed.
Select the check box(es) next to the fields that you want to designate as signed fields and associate with the signature. If changes are made to designated signed fields after the form is signed, the signature will be invalid.