FI Manual Invoice SmartForm, Document Number Value

Dear All,

I have a requirement of developing a SmartForm for FI Invoice.

The problem is, i need the value of Document Number(BELNR) from print\driver program.

The print program RFKORD50 is developed in scripts.

Kindly suggest how i can obtain the value of BELNR from print program, if i am writing the logic inside SmartForm.

If not possible, how i can use the standard print program RFKORD50 for the same.

Waiting for your valuable inputs.

Regards

Vik