Mary,
No problem - although I'm now shuddering at the typos and malapropisms in my previous message! eCommerce is pretty complex. I've been involved in website design for nearly two decades and I still find it one of the most complex of web disciplines. There are a lot of components to bring together - invoicing, customer management, payment channels, stock managment, web site content management, and so on.
I have overlooked some options though. For one thing, you could relatively easily set up an eBay shop, await payment for documents via PayPal and then manually email your document to customers. Another option I often overlook (due to my obsession with free software) is the availability of commercial eCommerce packages and services. Many ISPs offer specific eCommerce hosting with a lot of stuff pre-set up for you, so that's worth a look. Or you could consider purchasing a packaged eCommerce product which would normally come with a lot of online help, to hand-hold you through the process of setting up your shop. I can't help you with choosing one unfortunately, since I have no experience with the paid products.
Just something else to think about, anyway. On low margin sales (as internet sales tend to be), costs have to be kept streamlined!