Use the_content
filter to add your fields to the output of the_content()
function:
function wpd_content_filter( $content ) {
if ( 'your_custom_type' == get_post_type() ){
if( $meta = get_post_meta( get_the_ID(), 'foo_meta', true ) ) {
$content = $content . $meta;
}
}
return $content;
}
add_filter( 'the_content', 'wpd_content_filter' );