TOPIC: Agile Practice Guide in PMBOK 6th Edition

I downloaded the PMBOK guide from PMI site. I can see the guide is divided into two books, 1. A guide to project management body of knowledge(PMBOK) and 2. Agile Practice Guide. Do i need to read both? I thought PMBOK( first book ) is modified to add Agile related process. Why there is a extra reading material for Agile as Agile Practice Guide ?

I would read all of it and at least become familiar with the content; you could be tested on it.