Acetic anhydride, like any anhydride, reacts with water to form a carboxylic acid. How is it then…

Acetic anhydride, like any anhydride, reacts with water to form a carboxylic acid. How is it then possible to carry out an acetylation in aqueous solution?What is the purpose of the hydrochloric acid and the sodium acetate in this reaction (synthesis of acetanilide from aniline and acetic anhydride)