ie. You can own the surface rights, but you sell the timber rights to farmer John for 25 years. The nature of the status of the land is fixed by law, and are distinguished as being either a freehold estate or a non-freehold estate. Freehold means ownership without limitations to duration.
The acronym PDF stands for 'Portable Document Format'. This long form of the acronym still doesn't tell you a lot, but it can give you a rough idea of what we are talking about. One thing that you can grasp easily is that it's a 'Document Format'.
A PDF is the file used to design your book for print; an eBook's main purpose, on the other hand, is to be read on an eReader. eBooks have a very different internal structure, and are meant to be manipulated. In fact, that's one of the biggest draws for people who use eReaders.