I have a little over 100 different PDFs at over 1.5GB I need to get up for sale on a website. What I'm wanting to know is, the easiest and FREE way to go about doing this on a Windows based server. I'm pretty sure this would rely heavily on asp and mysql, but I don't know about them. What I want to do is allow visitors to add PDFs to their shopping cart, check out through PayPal, then be redirected back to my site where their PDF(s) will begin to automatically download. I would like:

the download to expire after a few hours/days
the PDFs to be encrypted
download links to be inaccessible
maybe a script to generate a session id/pass for access to only the PDFs they bought

I'd like to know what all is feasible, if any. Links to tutorials would be great!