Pete Fuhrmann,
In order to auto-generate a unique sequential number for the PO every time the form is opened, you would need something external to the form that stores the latest PO number used. This means you would probably connect your form to a database or web service that stores the value. You can connect a form to a database or web service by creating a
data connection.
Note that while data connections are pretty much the only to get data into your form,
importing data is not possible by default in the free Reader.
Stefan
Adobe Systems
More answers at
Stefan Cameron on Forms.