Set subform field only to Display

Set subform field only to Display

Hi ZC Team
I have a Form with a subform, when I click on Add I have a field on the subform that is completed with a value existing on the parents form. What I want is to show as today but disable the possibility that the user update that Field (is a dropdown field)
I was trying at subform level on Load Add disable but it doesn't work, is any way to only display a field in subform and avoid alter it?, please let me know.

Thanks a lot.

 
Victor Miranda