The read only option allows you to configure certain form fields to be set to a read only state. Fields set to read only will be visible but not editable. In other words, the user can “read” the field value but can not change the field value. This is useful in situations where you would like to present information to the user without the user being able to modify that data.
1) The read only setting can be enabled by navigating to the “Appearance” tab on an applicable field. This will work for text input, textarea, checkbox and radio button.
2) You will need to add a custom class to your field to easily target the field. Add a class name of gf_readonly to the Custom CSS Class field.