Catalyzes the hydrolysis of N(4)-acetylcytidine (ac4C). H2O + N(4)-acetylcytidine = acetate + cytidine + H(+) H2O + N(4)-acetyl-2'-deoxycytidine = 2'-deoxycytidine + acetate + H(+) H2O + N(4)-acetylcytosine = acetate + cytosine + H(+) Belongs to the N(4)-acetylcytidine amidohydrolase family.