Infopath 2010 - Forms

To make a form Read-Only

To make a form read-only, add a property named readonly to your schema that will be set to true when the form is submitted.

Adding a rule into the form load event which switches active view to read-only view, if this readonly property is set to true, will always show the read-only view after the form is submitted.

Source: Expert SharePoint 2010 Practices, Apress Edition