Hello Cheryl,
Check below steps. In regards to PDF format, so I am not sure if that is possible? I understand from some users that this option is used only for selected customers and they prefer in below format through FBL5N which gives them filter/layout options for those exceptional customers.
Execute FBL5N,
Select invoices which you wanted to send (You will need to use filter option).
B/R
Prashant Rane