Is there a way in RE 7 to generate invoices on pledges that are put into RE? 

I think the "RE term" you're looking for is 'billing reminders.'  And yes RE can generate reminders/bills/invoices.  It is a function on the MAIL tab.  You can use Blackbaud's forms or develop a custom form with whatever info you desire.  I use the function for monthly reminders and for donors who indicate on their pledge card that they want to be sent a bill.