Really depends what works for you and the nature of the assessment.
You might be asked through the instructions given to you to not use other software and then copy and paste your answer in. In that situation, you’d need to type in the platform as you go. But you could potentially use written notes rather than on Word to do this instead.
If you are allowed to copy and paste from another platform you could do this, but I would do an early test of the platform (early on in the exercise timeframe) that this works, as sometimes certain formatting can go a bit funny when transferred to these platforms, and you may lose things like bullet point or italic formatting.