Is the word Navajo a noun or pronoun?

The word Navajo is a noun, a proper noun; the name for the Navajo people of the southwestern US and the town of Navajo, NM. The word Navajo is also a proper adjective, for example Navajo language or Navajo art.

A pronoun is a word that takes the place of a noun; for example:

The Navajo are known for many crafts. They make world famous silver and turquoise jewelry. (The pronoun 'they' takes the place of the noun 'Navajo' in the second sentence.)