Hello,
How does a purchase turn into a subscription?

In other words:
How will I know there's a subscription? (Orders table? Other places?)
How can I differentiate between several different subscriptions?
How do I go about locking subscriptions to eBooks?

(Our client has PDF's that they want to be available via subscriptions and open only in the site. I realize PDF 'save as' capability, this is just what they want.)