HI Bruno,
In case of smartforms you will find 3 tabs in the left side such as
1)Attributes
2)Form Interface
3)Global Definitions
The form interface is the exact place in which your smartform is linked to the driver program.
The parameters/variables present in the driver program will get reflected in form interface. You will get the PO and SO details in the Form Interface only .Using the parameters from form interface you will process your logic and display the details in smartform.
Thanks,
Kotni Srikant