I'm not quite sure how they've done it, but the Czechs have done pretty well at hanging on to their historic documents. They've got the founding charter of Charles University and the Declaration of the Estates of Bohemia, with the original seals. The latter is especially impressive, since there wasn't room enough on the Declaration itself for all the seals, so they tore the bottom into little strips and each noble affixed his seal to one of the strips.
The best, though, is one particular imperal decree for religous toleration. It's in several pieces in the display case -- because a later Habsburg emperor publicly tore it up as part of his campaign of re-Catholicization.