I'll help you include the P.O. number in your estimate, @jim85.
Custom fields allow you to record what is relevant to your business and customers. We can create a purchase order number box in the custom fields to show in the estimates.
Here's how:
On the top right corner, go to the Gear icon.
Select Custom fields under Lists.
In the Custom Fields page, choose Add field.
Enter the P.O. box number under the Name box.
Tick the All Sales forms box below the Select form type.
Once done, click Save.
After this, you may create an estimate and enter the P.O. number in your form. Please note that you may create up to 12 custom fields for each form.