def cleanFileName(fileName='defaultName'):
    """ Processes a string name into a filename removing invalid tokens.
    Args:
        fileName: string name
    Returns: clean name
    """
    pdfName = fileName
    validchars = "-_.() "
    pdfNameClean = ""
    for charItem in pdfName:
        if str.isalpha(charItem) or str.isdigit(charItem) or (charItem in validchars):
            pdfNameClean += charItem
        else:
            pdfNameClean += "_"
    return pdfNameClean