Learn Russian: Она распечатает текст и вернёт его степлер. - She will print out the text and return his stapler.

Его is a third-person possessive pronoun meaning "his". Unlike words for "my" or "your", the words for "his", "hers", and "theirs" (его, её, их) are indeclinable. They keep this exact same form regardless of the gender, number, or case of the noun they describe.

Why do распечатает and вернёт translate to future tense ("will print", "will return") without the word будет?

Both распечатать and вернуть are perfective verbs, meaning they focus on a completed result. When you conjugate a perfective verb with normal present-tense endings, it automatically acts as the future tense. You only use будет with imperfective verbs.

What case are текст and степлер in?

They are both in the accusative case because they are the direct objects of the verbs (they receive the action). Because they are masculine, inanimate objects, their accusative forms look exactly the same as their nominative (dictionary) forms.

How does the prefix рас- change the verb печатать?

The base imperfective verb печатать means "to type" or "to print" in a broad sense. Adding the prefix рас- creates the perfective verb распечатать, which specifically means "to print out" a physical hard copy of a document.