Post Title to link to a PDF

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I recommend using the plugin Advanced Custom Fields (Very popular plugin).
It lets you create fields and manage their values very easily.

This way you could just create a new field for file upload and then to pull its information like this-

<?php
    $my_file = get_field('my_file');
    if( $my_file ) {
        echo $my_file['url'];
        echo $my_file['alt'];
        echo $my_file['...
    }
?>