I've just got the most excellent Ubercart ecommerce system to work with Paypal for paying and then auto-downloading digital media (eBook).
I thought I would jot down the process, as a memory jogger for me and if it helps anybody out there in inter-web-cyber-highway-net-land then it's worth the wasted minutes of typing ;)
So lets start with the basics, obviously replace http://the-pc-workshop.com with your own website name... duh!
- Install ubercart - a simple download and upload to your server into the ../SITES/ALL/MODULES folder
- enable ubercart and related modules Workflow-NG, Token, Content, CCK Image field, and the Imagecache modules.
- enable the ubercart modules components (http://the-pc-workshop.com/admin/build/modules) and activate cart/order/product/store and filedownloads/notify/payment and a payment method like Paypal
- setup the store with your details (click STORE ADMINISTRATION from the admin menu http://the-pc-workshop.com/admin/store)
- import all the country code address formats from http://the-pc-workshop.com/admin/store/settings/countries/edit
- configure the payment settings http://the-pc-workshop.com/admin/store/settings/payment/edit/methodsand select Paypal standard - enter your paypal account name and select LIVE
- make sure the FILE DOWNLOAD option is active in the MODULE LIST (note that I have 3 different columns for User authority in my configuration (Admin, AnonUser and Registered) just make sure Anonymous user can download.

Note: if you are getting ACCESS DENIED messages when trying to collect your digital media (as a customer) then you've probably not done this step.
- define the folder that will contain the digital media (ebook, file, ZIp or whatever) that is being sold and automatically downloaded to your buyer. Note: I created a folder in my website called stuff and a subfolder called ebook for this example and uploaded my digital media to this folder: dont worry we will link the product to this item in a minute.

- You can upload/download files into your digital media folder (that you have just defined) using Drupal here http://the-pc-workshop.com/admin/store/products/files
- Last (but not least) you need to setup the notification settings so that your customer is emailed a link for the download of the digital media they have purchased.
- So goto http://the-pc-workshop.com/admin/store/settings/notify/edit/file and click the send email check box. By default, the file download (and email) is sent once the order moves to "completed" status. But I have found with Paypal it's better to have this email sent immediately that it's paid for so change the setting here http://the-pc-workshop.com/admin/store/settings/products/edit/features.
Basically THATS IT!!!
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