Documents and sources
Acta Pacis Westphalicae: In 1957, the Vereinigung zur Erforschung der Neueren Geschichte (Association for Research of Modern History) was founded with the idea of publishing correspondence and other documents relating to the Congress of Westphalia. More than 50 years later, it has published over 40 fat, well-edited volumes on French, Swedish, and Imperial correspondence, protocol of councils, diaries, and other documents — an incredible trove of research for the historian. In 2014, the made this amazing collection available in digital form. Historians of the Peace of Westphalia owe them a huge debt of gratitude — and by “them” I mean everyone who has participated in the project, but especially Prof. Dr. Konrad Repgen, who headed the VENG for nearly 50 years.
An English translation of half of the Peace of Westphalia — the treaty between France and the Holy Roman Empire — is available at the Avalon Project. This is, however, a poor alternative to the version published by the VENG and also available online. There, you can get the full text of both documents, in the original language and in English translation, in parallel if you want. There are also translations in German, French, and other languages (and the translated version sometimes carries as much historical weight as the Latin original).