English Translation
I am to examine the documents once more.
～なければいけません doesn’t capture the nuance of “be to do” in English. The Japanese translation is closer to “I SHOULD examine the documents once more”. The speaker recognizes that the it’s his duty/obligation. But he doesn’t say he is actually going to fulfill the duty.
My alternative translations are:
私はもう一度その書類を調べるつもりです。or
私はもう一度その書類を調べることになっています。
Both suggest that the speaker is going to examine the documents. My first translation implies that I am happy to or fully motivated to examine the documents. My second translation with ことになっています implies that the duty is assigned by someone (senior) – i.e. passive.
You can also replace 書類 (documents) with 資料（しりょう）or 文書（ぶんしょ）.