Hi Madhavi,
I am assuming that after saving Invoice in VF01 that transaction should be navigated to VF03 carrying the generated invoice number. Sorry, if my assumption was wrong.
For this, I believe by the time this exits executed the Invoice number will not be generated. So, I suggest you to go for Implicit enhancement. Check in debugging when the Invoice number is getting generated and after getting Invoice number, set that as Parameter Id of 'Document Number' field in VF03 and then call transaction VF03 by skipping its first screen.
Regards,
Vijay