// http://www.gravityhelp.com/forums/topic/conditional-logic-for-user-notifications
// update the "2" to the ID of your form
add_filter('gform_pre_submission_filter_2', 'conditional_message');
function conditional_message($form){

        // update the "7_1" following "input_" to the IDs of your fields
        $choice1 = RGForms::post('input_7_1');
        $choice2 = RGForms::post('input_7_2');
        $choice3 = RGForms::post('input_7_3');

	// if any box was checked, say thank you.  Since field is required, this will always test TRUE
        if($choice1 || $choice2 || $choice3)
                $form['autoResponder']['message'] .= "Thank You";

        // append a different PDF link based on the interest
	if($choice1)
		$form['autoResponder']['message'] .= "<p><a href='http://kreatorsafety.com/uploads/belt_guard.pdf' title='Download your free Belt Guard Data Sheet'>BELT GUARD DATA SHEET DOWNLOAD</a></p>";
	if($choice2)
		$form['autoResponder']['message'] .= "<p><a href='http://kreatorsafety.com/uploads/coupling.pdf' title='Download your free Safety Guard Data Sheet'>COUPLING GUARD DATA SHEET DOWNLOAD</a></p>";
	if($choice3)
		$form['autoResponder']['message'] .= "<p><a href='http://kreatorsafety.com/uploads/K.S.Catalogue.pdf' title='Download your free Catalogue here'>SAFETY GUARD CATALOGUE DOWNLOAD</a></p>";

        // return modified form
        return $form;
}