Hello, Gabriel. Yes, you can definitely use any of the text in this pamphlet in your game.
If you do, please put this text in the copyright page of your game, "... based on The Magic of Names by Thomas Manuel which is itself based on Trusted with Its True Name: An Ethical Approach to LeGuinian Magic for Games and Stories by Victor A. Gonzalez and is licensed under a CC BY SA 4.0 International License."
Thank you!