I have to change a webpage content source, and obtain it not from DB, but from an exterior file. I have made the decision give a custom area 'staticfile' to page I wish to change source. I Quickly authored small-wordpress plugin and added there filter "the_content":

add_filter('the_content', 'static_content');
function static_content($content) {
    $custom_fields = get_post_custom();
    $my_custom_field = $custom_fields['staticfile'];
    $upload_dir = wp_upload_dir();
    foreach ($my_custom_field as $value) {
        if ($value) {
            $file = file_get_contents($upload_dir['basedir'] . '/staticpages/' . $value);
            return $file;
        }
    }
    return $content;
}

It really works fine excepting one factor. The html-code I recieve on ouput isn't strained. For instance, shortcodes added with another plug ins does not work. I attempted to create:

return apply_filters('the_content', $file);

However it breaks all output (most likely it loops the code). It is possible to method to change supply of page with using filters?