redirect the page based on the shortcode attribute

note.txt

The meta refresh is bad coding standards, but all browsers support it and it works. 
The javascript is fallback redirect, and the html link is double-fallback. 
Now you could make the redirect happen before the document headers by tapping 
into a early hook like wp_loaded, seeing if the user has proper password with a 
function or two, and interpret the $post->post_content shortcodes yourself then 
properly redirecting with wp_redirect() - but the lazy way I've done works too.

WP-redirect-a-shortcodes-url-attr.php

<?php

add_shortcode( 'pdf_redirect', function ( $atts ) {
    $a = shortcode_atts( array(
        'url' => '',
    ), $atts );

    // instructions in case of misuse
    if (empty($a['url']))
        return "<pre>Please assign a destination for the PDF redirect, [pdf_redirect url='https://yourpdfurl...']</pre>";

    return "
    <meta http-equiv='refresh' content='0; url={$a['url']}'>
    <script>
        window.location.href = '{$a['url']}';
    </script>
    <p>If your browser hasn't redirected you, please <a href='{$a['url']}'>click here</a>.</p>";
} );

// [pdf_redirect url="http://example.com/file.pdf"]