We read a lot about "soft power", but not in the PMBOK. It's not a power paradigm of PMI.
Soft power is a concept developed by Joseph Nye of Harvard University to describe the ability to attract and co-opt rather than coerce, use force or give money as a means of persuasion (Wikipedia)Attract and co-opt rather than buy your way in... what a concept! And, cheaper.
What does it take to put such an idea into practice? In a word: Leadership!
What's the word cloud for leadership? Here's one list:
Check out these books I've written in the library at Square Peg Consulting