File/attachment name dynamically changed

Hi developers,

I am trying to have the name of the report, which is attached to an email as a PDF file, changed dynamically, to reflect invoice number.

I am using SMTP to send out invoices attached to email, using print management and address tokens.

I got the subject line to change dynamically, to include invoice name and number. Any ideas how to change the report name? 

Would it be better to change the file name, after the report is created and placed into the temp folder from where it is picked up to be attached, 

or, to change the report name when it is created?