Go into Admin > Extra Fields
DPO will allow you to have 3 extra fields, in order to set up an extra field click onto the pencil icon next to each extra field and enter the name of the extra field you would like.
If you would like to make this extra field visible then tick the visible checkbox so users will see this extra field when creating PO's.
In this instance we have created 3 extra fields which are labelled as:
When creating a Purchase Order, the extra fields will appear when adding a new line item like shown below: