Hi,You can print a purchase order from the action menu
Purchase -> open a PO Order -> action -> print-> purchase order
Below attached a screenshot on version 17

Hope it helps

Option 1

Go to Purchase > select/check the PO you want to download > on top print button will appear that would download your PO

Option 2

Go to Purchase > click on the PO > Click the gear on the left under Request for quotation > hoover on print > click on purchase order. that would download your PO