No, the word 'masterful' is an adjective, a word used to describe a noun.

A pronoun is a word that takes the place of a noun in a sentence.

The noun form of the adjective 'masterful' is masterfulness.

The word 'masterful' is the adjective form of the noun master.

Example use of the adjective 'masterful':

John Williams wrote a masterful score for the Star Wars movies.

Example use of a pronoun:

Williams won an Oscar for it. (the pronoun 'it' takes the place of the noun 'score' from the previous sentence.