The best way to keep documents is to put them in an environment where the temperature and humidity is stable. The paper is very sensitive to changes in temperature and humidity. These changes create tensions that can cause binders to crack and paper to tear. In addition, documents must be placed in containers made of acid-free cardboard.
Acid containers can accelerate the aging process of paper. (Acid-free boxes are available in artist stores.)
For paper handling, it is good to put each document in acid-free cardboard folders or transparent folders made of Melinex. (Still available in artist stores)
The site by the Canadian Conservation Institute explains in great detail what to do for the conservation of different types of objects.
Conservator, Preservation Section
Bibliothèque et Archives nationales du Québec
2275, rue Holt
Montréal (Québec) H2G 3H1