Great post Murtza! Colby, the iframe would preserve the part where after submitting the form you are redirected to a PDF. We used iframes on our site for a long time.
Of note, if you want to pass through URL parameters from the main URL to the iframe you will need to do some coding. Also, make sure your Google Analytics is set up properly. You don't want to have page views counted twice for every visit to the page with the iframe.