Do you know of any third party FTP services in which I may consider as a secure site to upload my digital products and reference with digital file pro? Also, if I am ultimately unable to secure my documents, is it possible to insert code that will redirect the user to my login page? 
Do you, perhaps, mean hosting services? FTP is just file transfer protocol - or the means in which you move files around to the server and back and forth.
If you are looking for hosting that allows "below root" publishing, I would recommend a company like Little Oak: www.littleoak.net/
They have tremendous customer support, uptime is great, features are spectacular, and the cost is great too considering the kind of support they have. And I think they have what you want... on the main account, you have the Primary folder. Under that is your "www" folder which will hold your documents accessible to the public. But, you can also create as many directories as you like under the primary and you can password protect those directories however you see fit.
Best regards,
Brian
