Conditional PDF

// update the "19" to the ID of your form
add_filter('gform_pre_submission_filter_19', 'conditional_message');
function conditional_message($form){

        // update the "3" following "input_" to the ID of your field
        $interest = RGForms::post('input_3');

    // append a different PDF link based on the interest
    // I used values to avoid capitalization and spaces in my values
    switch($interest) {
        case 'beltguard':
            $form['autoResponder']['message'] .= "<a href='http://www.example.com/whitepapers/belt-guards.pdf' title='Download your free Belt Guard whitepaper'>Belt Guards</a></p>";
            break;
        case 'safetyguard':
            $form['autoResponder']['message'] .= "<a href='http://www.example.com/whitepapers/safety-guards.pdf' title='Download your free Safety Guard whitepaper'>Safety Guards</a></p>";
            break;
        case 'catalogue':
            $form['autoResponder']['message'] .= "<a href='http://www.example.com/whitepapers/2011-catalogue.pdf' title='Download your free Catalogue here'>Catalogue</a></p>";
            break;
    }

    // return modified form
    return $form;
}