Learn Hardcore Russian: Завтра я прочитаю все документы.

прочитаю is the perfective future form of прочитать (“to read through”). It indicates a completed action.
читаю is the imperfective present (“I am reading”) and cannot by itself mean “I will read” in the sense of finishing the job.
If you wanted a general ongoing future action (without emphasis on completion), you’d say я буду читать все документы.

How do you form the future tense of perfective verbs in Russian?

Perfective verbs use a synthetic future (one-word) form by conjugation. For прочитать (infinitive) you drop -ть and add endings:
– я прочитаю
– ты прочитаешь
– он/она прочитает
…and so on.
That single word already carries the meaning “will do and complete.”

What if I want to use the imperfective aspect to talk about the future?

Imperfective verbs cannot form a one-word future. You use the periphrastic construction быть + infinitive:
– я буду читать (I will be reading)
– мы будем обсуждать (we will be discussing)
This focuses on the process, not its completion.

Why is документы in the form (and not, say, )?