Use the Past Indefinite or the Past Perfect.
He (to understand) the book only after he (to read) it again.
I didn`t know that woman. I never (to see) her before/

I never saw her before.( я вот на счет этого предложения сомневаюсь)Может пересмотрите?

хорошо , сейчас еще посмотрю на всякий случай

спасибо)

нет , скорее всего там i had never seen her before , я не обратила внимание на before , это же показатель Past Perfect , да , вы правы

спасибо большое, вы мне очень помогли)))

He understood the book only after he had read it again

I had never seen her before

He had understood the book only after he had read it again

I didn't know that woman. I never saw her before.