I didn't realize it was for documentary as well. Thought it's just some kind of new genre 'Mockumentary' comedy.
Thought they were taking big risk by filming it that way without the classic laugh tracks and full of awkwardness, but it works.
There were some scenes when the cameraman wasn't allowed, like it was shot through window blind, or we only hear whispers behind close doors. So initially I thought it was part of DM documentation only, some kind of office practice and policy exclusive to DM weirdness. However when we see other branch's stories, they seem 'proper', so maybe it's more to reality TV of Scranton DM. Why anyone think it's a good idea on that fictional universe, I don't know.
But I like the show.
Haven't tried the British version too, except half of first episode and tbh, didn't really pull me in. But back then I dislike almost all British shows.