def METHOD_NAME(app, docname, source):
    """ prepend header to every file """
    section = "manual-%s" % app.config.language
    header_file = config.get(section, "header-file")
    if header_file and os.path.exists(header_file):
        with open(header_file, "rb") as f:
            source[0] = "%s\n%s" % (f.read().decode('utf-8'), source[0])