Expectation by the user is that they will receive a White Paper if
they provide their own details. If they have to press another button,
that is annoying. If they see a button that suggests more steps that
can be a stopper as the User may think there are more hoops to jump
through. Exit User; lost conversion.
I can't see why submitting a form and allowing download is NOT
conversion. It will be tracked in the logs anyway. Apart from showing
that they REALLY want the White Paper by clicking again on another
button I don't see the benefit. The odds of somebody going to the
trouble of filling in details and then NOT clicking on a button to
download the White Paper I would say are slim. Make download
automatic and keep the process as painless as possible.
However you should still have a button to download the White Paper on
the Thank-you page IF the download does not commence in a reasonable
time or is interrupted. And you should also push other White Papers
that may be of interest to the User on the thank-you page as well
that the User can download directly. The User has committed their
information you, so give them a few extra golden nuggets is always a
good customer building thing.