Welcome, hangupsinc!
It sounds like you have a rare & valuable page to frame. So, it's important to not change its condition, and to protect it from anticipated hazards, such as light, and temperature & humidity changes.
Ron beat me to it -- a clear polyester film "encapsulation" mount is the way to go.
But here are a couple of additional thoughts:
1. Use Tru-Vue's new Optium Museum Acrylic on both sides. This is Cyro Acrylite OP3, UV-filtering acrylic with the anti-reflective Museum coatings. It is of course more expensive than other glazing choices, but in relatively small size jobs like this one, the added cost is far outweighed by the visual enhancement it provides. And it's lightweight, too.
2. Use at least a double mat on both front & back, to provide at least 1/8" air gap between the glazing and the mount.
3. When you create the mount, use only Melinex 516 or its predecessor, Mylar-D. Be sure to avoid substitutes, because no other clear film is equal to these -- except Hostaphan 43-SM, in Europe.
4. To attach the two sheets of clear film together with 3M #889 double sided tape. This is the thinnest polyester tape I've seen, and it has a good acrylic adhesive; non-migrating & inert.
5. Place the tape strips only on the film, no more than 1/4" away from the the perimeter of the document, and no closer than 1/8". Make sure no tape touches the document, and sandwich the sheets of clear film together carefully.
6. Cut your mat opening so that the edges of the document show, and the tape lines are covered.