From The Library of Congress:
Proper Care and Handling of Works on Paper
Works on paper generally refer to flat (as opposed to bound) paper materials, including documents, manuscripts, drawings, prints, posters, and maps. Taking care when handling any collection item is one of the more effective, cost-efficient, and easily achieved preservation measures.
Take proper care when handling flat works on paper by:
- Having clean hands and a clean work area
- Keeping food and drink away
- Using pencil, not ink, to make any necessary marks or inscriptions; in addition, only make inscriptions when the paper is on a clean, hard surface, to avoid embossing the inscription into the paper, which will be visible from the other side
- Not using paper clips, other fasteners, “dog ear” folding to mark or organize leaves
- Not using rubber bands, self-adhesive tape, and/or glue on paper
Proper Storage of Works on Paper
Good storage significantly prolongs the preservation of paper materials and includes:
- A cool (room temperature or below), relatively dry (about 35% relative humidity), clean, and stable environment (avoid attics, basements, and other locations with high risk of leaks and environmental extremes)
- Minimal exposure to all kinds of light; no exposure to direct or intense light
- Distance from radiators and vents
- Supportive protective enclosures*
- Unfolded and flat or rolled storage for oversized papers
- Individual/isolated storage of acidic papers to prevent acids from migrating into the other works on paper
* Supportive protective enclosures include: acid- and lignin-free folders, mats, and document boxes (all available alkaline buffered or neutral pH); and polyester film sleeves that are stiff enough to adequately support the paper(s) within. Alkaline buffered storage materials provide a desirable neutralizing effect on acids that are inherent in works on paper, especially as paper ages, but be aware that some media found on paper objects may be sensitive to alkaline pH. Polyester film has the benefit of being clear, but does not contain an alkaline buffer and with little friction readily produces an electrostatic charge that can lift powdery media such as pastel, charcoal, pencil, and flaking paint.
The Northeast Document Conservation Center 
has put together very useful technical leaflets on storage solutions for paper artifacts. Folders, boxes, plastic sleeves, and other supplies for the proper storage of paper artifacts can be purchased from preservation suppliers.
Dealing with Condition Problems
For condition problems that are insufficiently addressed by the measures outlined above, conservation treatment by a paper conservator may be necessary.
The national professional association for conservators, the American Institute for Conservation of Historic and Artistic Works (AIC), maintains an online directory for finding a conservator by specialty and geographic location and provides information on how to choose a conservator. In addition, AIC also offers guidelines for the care of collections beyond library materials.
Link to the rest at The Library of Congress
Preservation Week, sponsored by the American Library Association, ran from April 25 – May 1, 2021 (Yes, PG missed it). There is lots more information about preserving all sorts of documents, audio, video, etc., at the Preservation Week website.