As Ananais mentioned last year, we don't plan on offering a PDF version of the School of Pipsology. The last PDF was available in 2008, and we supported existing PDF buyers until late 2009.
While it makes sense to the many readers that want offline access to the School lessons to bring back the PDF, Mr Gone explained it perfectly above. Keeping the PDF updated and available to our readers was very troublesome in the past. With additions and changes to the lessons happening frequently, we didn't have the resources to manage the PDF as we would have liked. So we discontinued it.
We can make changes instantaneously on the web, so there's no waiting and no downloading on your part. With Internet speeds getting faster, and more users moving to mobile (tablets, smart phones, phablets, laptops) and Internet-ready devices, it's easier to access online content from anywhere, at any time.
We think we've struck a good balance between availability and user experience (at least we hope so!). But to reiterate, we have no plans to bring the PDF back. The School will only be available online.