This is possible with our premium add-on ATUM Export PRO using the Purchase Orders entity. I recommend you to create one Purchase Order, export it, and use this one by default in order to know how to create the new purchase orders.
Note you have to use the INSERT option. Also, take into account that even you can import new Purchase Orders, the stock of the products won't be updated.
I leave you here the documentation of the add-on where you will find useful info about how it works: https://forum.stockmanagementlabs.com/t/atum-export-pro-documentation
And the link to the demo site in case you want to try the free trial: https://stockmanagementlabs.com/addons/atum-export-pro/