Field is only visible when on "Writing" mode

I have the following field in my Django Admin app:

class ContractForm(forms.ModelForm):
    ativo = forms.CharField(
        initial="this is a test"
    )

The field value is visible when the logged user has all permissions (can add, change and view) on Admin's default auth console:

But when the user has only view permissions, the value is not shown:

Any thoughts?