Yes. 'must' and 'must not' (/mustn't) are imperative. Unconditional orders (/regulations). 'You must not press this button!' = You are not allowed to press this button. The opposite: 'You must sign here.' = You have to sign here.

Hello Jane , Yes it is correct and a synonym to " don't have to " You must not do that = You don't have to do that .

Yes, I use it very often!