You will record the world & edit the footage.
This, to many, represents "reality."
But, of course, recording & editing is subjectivity in action.
Meaning, the movie is no longer an accurate representation of reality.
The camera is from a particular point of view, and the editing takes specific moments from a particular point of view and arranges them in a specific order.
What was once "reality" is now subjective - something aesthetic, filled with personal meaning.
Because reality can never be reached in a documentary, I suggest your goal be entertainment.
For the social activists among us who find this idea repulsive ("BUT I WANT TO WAKE PEOPLE UP!" they say) I suggest, more specifically,
A good documentary is 80% entertainment and 20% information.
People want to be entertained, not educated.
(But education is important, so feel free to sneak it in.)
So how does post-production sound design fit in?
Well, once the movie is edited, it's going to require what I call a "sound design pass."
You watch the movie and listen to the points where the flow or overall rhythm feels thin, or lacking in substance.
This is usually signified by you (or another viewer) shifting in their seat, reaching for their phone, looking at the time, or checking the duration left in the movie.
It's these points you want to beef up.
And a good trick for this is sound design.
Be liberal with the adding of ambience, the sounds of cars passing by, accentuating laughter or applause at the perfect moment, kids laughing in the background, etc.
I often get a note from my peers that they love when a certain sound syncs up with the action in one of my documentaries, and they can never tell if I placed it there myself or if it was naturally recorded.
Makes the movie all the more wizard.
You can do the same by becoming aware of your documentary sound design.
It's going to add SO MUCH to the experience.
Primarily, this effect creates a sonic wave of immersion for the audience's brain to fall into.
It's like a consciousness trap.
There's evolutionary reasons for this, which I'll talk about later.
It can also illustrate the substance of a scene without words .
Note any Nick Broomfield documentary - or even Ken Burns.
Two wildly different filmmakers, yet they both incorporate sound design like experts.
Watch "Baseball" (1994) or "Biggie and Tupac" (2002) and see if you can pick up on the extensive sound design foundation hiding almost slightly below our threshold of awareness.
You need not concern yourself with the "falsehood" of "altering reality" because there is no reality in the first place.