I have added aria-hidden="true" for span tag and converted it to PDF. Now I am trying to read the content inenter code here PDF using text to speech voice reader extension in google chrome.
<body>
    <span>
        This content is perceivable by screen readers.
    </span>
    <span aria-hidden="true">
        This content is not perceivable by screen readers.
    </span>
</body>