There is no active version of your original sentence, The closest logical one would be something like "People [mostly] make paper from wood".
I would say the best way to rephrase your example (if you must) in the active voice is: People make paper mostly from wood.
mostly is better next to from wood.
[These marks are called square brackets.]
Sorry I was not very clear. (These are round brackets.) [These are square brackets.]
Both kinds of brackets have multiple uses. Why don't you see if you can find an explanation of these uses online first, and then come back to us in a different thread if you still have any doubts.