A Sales Order can be cancelled when its status is still Pending Approval. It is not possible to restore (un-cancelled) a cancelled Sales Order. This feature is being tracked on Enhancement 28338: Allow cancelled Sales Orders to be restored (un-cancelled).
A Sales Order can only be closed after it was approved (Status = Pending Fulfilment). A Sales Order is closed when the user does not intend to fulfill open items on the order. The user can re-open a closed Sales Order by performing the following steps:
1. Navigate to Transactions > Sales > Enter Sales Orders > Lists.
2. Click Edit on the Sales Order.
3. Navigate to Items tab.
4. Locate the line item then remove the check mark on the Closed column.
5. Click Save.