Hi
Here are my answers to your questions :
As far as we can tell:
'Notification email' => It is the email which will be sent to site administrator when someone purchased documents from your site .
Notification Email Subject (For Free Download) => That is the email which will be sent to administrator when someone download free documents from your site. If you don't offer free documents, don't worry about it .
Confirmation email => This is the email sent to users after they purchased documents .
Pay later email => This will be sent if someone purchase document and choose Offline payment as the payment method. if you don't activate offline payment method, don't worry about it .
Order activated email body => This email only is sent if you enable offline payment method on your site. When someone choose offline payment method for your order, the order status will be set to unpublished and they cannot download documents yet. When they send payment to administrator (via bank for example), admin will activate order and this email will be sent. Again, you don't need to worry about it if you don't use offline payment method.
Order form message - shown in page => It is showed above checkout page .
Order Form Message (Cart feature enabled) => This message will be displayed above checkout page if you enable cart feature (when you enable cart feature, users will be able to purchase more than one documents within an order) . You can activate cart feature by going to configuration function of the extension, In general tab, look for Activate Cart Feature config option and set to Yes .
Confirmation page message - shown immediately before purchasor goes to payment gateway (order doesn't exist yet)
Thank you message - shown when purchasor returns from payment gateway (eg paypal)
Download form message <-- don't know what this is => It is only showed when someone download free documents. Don't worry if you don't offer free document
Download Complete Message <-- This is for downloading free docuemnts.
Cancel Message <-- When users go to Paypal and decide to cancel the order (they don't make payment), they will be redirected to cancel page where this message displayed .
Hope my explanation is clear to you . Please let me know if you have more questions .
Thanks,
Tuan