Hi Ghochh,
I’ve used all the major WP Plugins like WP Commerce but they’re usually a huge pain to customize and configure… especially for things like digital products.
Depending on your level of coding expertise you may want to consider rolling your own order form for this or you can hire a company that can do it for you. Most web developers who are trained in SSL can do this or you can try the route we ended up taking… we found a company called Secure Order Form that offered to build a custom system for us when we signed up for their services. It was pretty good and gave us all the features we needed.
Someday I’m sure WordPress will have better ecommerce capabilities but in the mean time I hope you find a solution that works for you!