How to make DFFs read only at invoice header lever

Summary:

One of my clients has a requirement whether some DFFs populated on invoice additional can be ready only.

DFFs all need to be only readable but not editable.

We integrate some data with the corresponding attributes linked the DFFs accordingly.

Hence, We just want to view the imported values on DFFs, but not modify them.

I gave it a try using sort of sandbox or something like that, but I have no idea about how to do that to the begin with.

it will be really thankful of me if anyone provide some guidances which enable my requirement done.