def _isPDF(zipItem):
    """
    Check whether an item in a ZIP file is a normal PDF file.

    This ignores metadata added to ZIP files on Mac OS X.

    :param zipItem: An item in a ZIP file, such as those returned by zipfile.infolist().
    :type zipItem: zipfile.ZipInfo
    :return: True if the item is a normal PDF file.
    """
    filename = zipItem.filename

    # Ignore Mac OS X metadata
    if filename.startswith('__MACOSX'):
        return False

    return filename.lower().endswith('.pdf')