See, Buyer generates the Purchase Order and send it to the Vendor through Email, Fax or hard copies,
to have a proper communication.
And now comes to your Vendor, Vendor get this in the form of soft copy (Email) or hard copy (Fax or Printouts).
There is no alternative, PO you must have to send to the Vendor, otherwise it will create miscommunication.
The choice is your's that you want to send the soft copy or hard copy.
And this you can control in message output type in the Purchase Order document.
Hope, it's cleared now.