What conventions do documentaries share?

There are many conventions that documentaries share.
Voiceover: these will typically be informative, may include interview answers, answers that have been prompted from a question. This will be on a fairly specific topic. This will make the audience feel as if they have very specific knowledge. Authoritative voices tend to be used, to show the power of the filmmaker.
Footage: This footage will generally include lots of seemingly raw footage, It has been made to look like it has been made and barely edited, because this gives it an edge that means it is more realistic than a trailer or something that has been touched up a lot.
Use of titles: These are also used for an informative use. Usually titles within documentaries are used for statistics and filling people in on information not used in a voiceover. It is a good way of conveying and reiterating information.
Interviews: provide different insights into the thing being captured. Usually filmed in a close up or mid shot. Graphics are conventionally used to anchor who the person is and their relevance to being in the documentary.
There are six main types of documentaries. Expository means it doesn't follow the conventions of normal documentaries. Observational documentaries focus on just using one camera in order to capture the world, and this footage tends to be much more raw. Participatory documentaries include means the filmmaker is evident in the video. Reflexive ones are based on real life moments and objects, but are based more on opinions rather than real life facts. Performative documentaries are based mainly on emotions, and the filmmaker tends to react to the matter in hand. Lastly, poetic documentaries are a subjective representation of reality.
The lighting in different documentaries are different for different reasons. Low key lighting will be used for social mood and realism, medium key lighting will be used for idealistic realism and high key lighting will be used for documentary realism.
There are single stranded narratives which are non-linear. Normal cuts are used, so there aren't fancy over-edited shots because they are kept as raw as possible usually to keep straight to the point and are used just to capture what is going on.
This genre is good because it allows people to express their points of views and opinions as well as an illustration of the truth in a way which is flexible yet understood by audiences who have become accustomed to the conventions of the genre.