How to lock the data in richtext field?

Hi,I have a richtext field in notes form, now, I want to have a button on the action bar, when click it, the content in the Richtext field will be locked which can not be edited, something like computed for display only. For user with Admin role, they can still edit it.

Anybody knows how to program this? Thanks a lot,

Subject: Put into a section

Create a section around the field, and then put in a formula where only Admin can edit it.

Cheers,

John