GP6 - Can I pay for someone else, and what name must I write in the order form?

YES, you can order a Guitar Pro license for someone else. The person who registers his/her license is the one we'll consider to be the final user. So you can either directly write that person's name, e-mail and postal addresses in the order form, or yours if you prefer to receive the software and give it later to the person (as a gift, for example).