Depending on exactly what it is you're looking for, you may be in luck!

Specifically, the Peace of Westphalia comprised three treaties. The first (The Peace of Münster) was signed between the Dutch and the Spanish, in that city. An original copy of this treaty is located at the Nationaal Archief in The Hague. You can find pictures of it online, but the archive's reading room is closed until next year, and I'm not sure what particular restrictions they might have on this particular document.

The second treaty, the Treaty of Münster, was signed primarily by France and the Holy Roman Empire. The town hall serves as a lovely museum to the Peace of Westphalia, but you might be better served at the town hall museum in Osnabrück, where Sweden and the Holy Roman Empire participated in the Treaty of Osnabrück. Possessing a similarly lovely museum dedicated to the topic, the Osnabrück location does have a copy of the treaty signed there. It was on display at least as of 2018, though I couldn't say for certain in regards to 2020, especially with a lot of museums altering operations and exhibits due to COVID.

I hope this helps!