To answer this question you have to think about what causes deterioration. Deterioration is caused by time, life and chemical reactions mostly.

**Existent technology**

Storing them in a steril, void enviroment could conserve them indefinetly. This technology currently exists, though that i know of is not used for this particulary propose.

Vacuum tubes and light use this technology to avoid oxidation. Also some types of food are stored in vacuum to prevent their deterioration. 

https://en.wikipedia.org/wiki/Vacuum_tube

https://en.wikipedia.org/wiki/Vacuum_packing

There is also gas storage. Basically the document is stored in a very lethal and inert gas like argon that impedes oxidation and life. The Magna Carta is preserved in this way.

Some foods are also stored in inert non lethal gasses. Like potato chips.

https://www.magnacartacanada.ca/preserving-an-800-year-old-document-2/

https://en.wikipedia.org/wiki/Vacuum_packing

An inert gas is a gas that does not undergo chemical reactions under a set of given conditions.

https://en.wikipedia.org/wiki/Inert_gas

**Fictional technology**

If your advanced race is advanced enough they could control time in with tachyons. This is purely theoretically and the existence of tachyons hasn't been proved.

Gravitons: the particle of gravity. Is well now that gravity can slow time. If your race dominnes gravity they could literally stop time around the storage of the documents.

Other dimension: Simply a dimension where time does'nt exists.

https://en.wikipedia.org/wiki/Tachyon

https://en.wikipedia.org/wiki/Graviton