Exoglucanase that plays an important function in biomass degradation by catalyzing the hydrolysis of the non-reducing end beta-1,4-glucosidic linkages in cellulose and cellotetraose to release cellobiose. Hydrolyzes crystalline and amorphous cellulose but is inactive on hydroxyethyl cellulose, mannan, galactomannan, xyloglucan, arabinoxylan, arabinan, xylan, and pectin