Entering an order number

Hi,
I used to be able to enter an order number on my invoices.
I enter the number that is given to the customer when placing an order from my website.
Now I don’t seem to be able to enter a custom order number, it just has a search option.

Am I missing something?
Is there a way for me to enter an order number on the invoice like I used to be able to do?

Thanks in adavance.

Yes, you have missed newsletter articles and numerous forum discussions on this very issue. The program was changed when the ability to track sales order status was added. The old Order field is no longer free text. To do what you used to do, you will need to create a custom field.