OK, now I'm officially lost.
I believe that I need to create a page with the list of available documents for download and have an "add to cart" button for each.
Those documents are records in the products table and the document name is in the ProductLocation field.
On leaving that page with a Submit button or something of the sort will redirect to the orderdetails_results.php page created with and without the tutorial listed above and the download button there will download the documents.
Am I on the right track? and if so, how do I go about creating the page with the list of documents available for download?