Below are politer ways of saying 'must' which you can use in your formal business or professional pieces of writing:
It is used when both ordering people directly what they 'must' do and saying what thing(s) 'must' be done.
'You need to complete the form by 23 November at the latest.'
'The form needs to be completed by 23 November at the latest.'
It is only used when ordering people directly what they 'must' do.
'You are required to complete the form by 23 November at the latest.'
It is used when both ordering people directly what they 'must' do and saying what thing(s) 'must' be done.
'You have to complete the form by 23 November at the latest.'
'The form has to be completed by 23 November at the latest.'