7-dehydrocholesterol reductase of the cholesterol biosynthetic pathway reducing the C7-C8 double bond of cholesta-5,7-dien-3beta-ol (7-dehydrocholesterol/7-DHC) and cholesta-5,7,24-trien-3beta-ol, two intermediates in that pathway. cholesterol + NADP(+) = 7-dehydrocholesterol + H(+) + NADPH 7-dehydrodesmosterol + H(+) + NADPH = desmosterol + NADP(+) Steroid biosynthesis; cholesterol biosynthesis. Belongs to the ERG4/ERG24 family.