I achieved this by "tweaking" the "Product URL" facility.
If you edit the DEFINE:
includes/languages/english/product_info.php
PHP Code:
define('TEXT_MORE_INFORMATION', 'For more information, please visit this product\'s <a href="%s" target="_blank">webpage</a>.');
.. to something like:
PHP Code:
define('TEXT_MORE_INFORMATION', 'For more information, please download this product\'s <a href="%s" target="_blank">pdf file</a>.');
Then, when you ADD or EDIT a product dataset, just put the URL path as the path to its PDF file.