Final answer:
The cofactor required to convert DHF into THF is NADPH+ and ascorbic acid.
Step-by-step explanation:
Conversion of dihydrofolic acid (DHF) into tetrahydrofolic acid (THF) requires the cofactor NADPH+ and ascorbic acid. This reaction is catalyzed by the enzyme folic acid reductase in the liver. NADPH+ serves as the reducing agent, donating electrons to DHF to convert it into THF.