How do I use a custom function (CRM) to automatically copy custom data from Account to Sales Order?

I'm trying to copy data from custom fields in an Account to a new Sales Order when a new Order is initiated (before Saved or Created).

I've tried using a custom function but it appears that it will only run when the order is Saved (Created) or Edited.

Zoho is obviously able to do this with fields that are fixed. Is there a way to do it with custom fields?

Thanks in advance.