Use this code snippet on functions.php file of a theme to add pages to a WordPress RSS feed.

add-pages-to-wordpress-feed.php

/**
 * 2a_feed_request function.
 * adds any post type to RSS Feeds. In this example, we use 'post' and 'page' post types
 * 
 * @access public
 * @param mixed $qv
 * @return array $qv filter $qv variable
 */
function 2a_feed_request($qv) {
	if ( isset( $qv['feed'] ) && !isset( $qv['post_type'] ) ) {
		
		$qv['post_type'] = array('post', 'page' );
		
		// we could add registered custom post types as well, e.g. product or video
		// $qv['post_type'] = array( 'post', 'page', 'product', 'video' );
		
	}
	return $qv;
}
add_filter('request', '2a_feed_request');