PMI has withdrawn the PMBOK (r) Guide, Sixth Edition in both hard and softcopy formats as the combination of the Seventh Edition and their Processes Groups: A Practice Guide effectively covers what was in the Sixth Edition.
As far as I know, your only option is to look for a copy in a third-party bookstore such as Amazon.
I recommend referring to the latest version, PMBOK 7, as it reflects the most up-to-date practices and guidelines for project management. It introduces a more flexible, principles-based approach that can be really valuable in today’s dynamic project environments. You might find it helpful for your exam preparation and practice! Saving Changes...