public static function copy_pages_to_readonly_area($assignment, $grade) {
        $fs = get_file_storage();
        $assignment = self::get_assignment_from_param($assignment);
        $contextid = $assignment->get_context()->id;
        $component = 'assignfeedback_editpdf';
        $itemid = $grade->id;

        // Get all the pages.
        $originalfiles = $fs->get_area_files($contextid, $component, self::PAGE_IMAGE_FILEAREA, $itemid);
        if (empty($originalfiles)) {
            // Nothing to do here...
            return;
        }

        // Delete the old readonly files.
        $fs->delete_area_files($contextid, $component, self::PAGE_IMAGE_READONLY_FILEAREA, $itemid);

        // Do the copying.
        foreach ($originalfiles as $originalfile) {
            $fs->create_file_from_storedfile(array('filearea' => self::PAGE_IMAGE_READONLY_FILEAREA), $originalfile);
        }
    }