"must fulfil" is correct and usable in written English.
It is usually used to express a duty, obligation, or requirement that must be met. For example: "All employees must fulfil their contractual obligations to the company."
The EU says Turkey has still not fulfilled the "Copenhagen criteria", which set out basic democratic norms that candidate countries must fulfil.
Formally, Turkey must fulfil two more conditions.
"First, Greece must fulfil the conditions.
And now a grateful nation must fulfil ours.
He must fulfil the players' needs and keep them happy.
GPs must fulfil their basic duty of care.
If peer review is to work, each party must fulfil its side of the bargain.
To be sure of victory, the unionist campaign must fulfil the promise of its name.
Of course, there are a number of critical prerequisites Obama must fulfil.
Parliament has decided these issues and the courts must fulfil its will.
But under the ICC statute, the prosecutor must fulfil her functions independently.
