Do you want to create a submit button in InfoPath to submit the form to a document library? Is it?
Well, if so, you should go to "Controls" and create a "Button". After that, you need to create a data connection to submit data...Finally, you'll create a rule in you button...This rule will have two steps.."Submit using a data connection" (the data connection you've created) and "Close this form: no prompt" (to close the form - of course..hahah)..
Bye..
João Selarim