When you want to buy a specific product from the company, you raise a purchase order. Examples of raising a purchase order include the purchase of a boiler, a DG set, a Xerox machine, etc. In the purchase order, you need to mention equipment specifications, delivery address, installation charges if any, payment terms, etc. Additionally, if the equipment needs to be transported inland or overseas, you also need to mention INCO Terms.
When you give a contract to a service provider to provide services, you need to raise a work order. Examples of raising a work order include the installation of a plumbing system, refurbishing marble flooring, hiring training services of a training professional, and so on. In the work order, you need to mention the type of services, labor charges, materials to be used, etc.
In some companies, a purchase order is issued even when services are hired. This is because these companies are ISO certified, and staff have to use specific forms only; no forms are to be created on their own.
In your case, for the purchase and installation of software only, you need to raise a purchase order. However, if you want support services from that software company beyond the 'x' time period, you need to raise a work order.
I hope this clarification satisfies your requirement.
Thanks,
Dinesh V Divekar