We do not have enough data on this route to provide a reliable graph showing how many days before departure it is the best to book.
However, usually the closer it is to the departure, the more expensive the tickets are.
The cheapest flights you can book on the route Charles de Gaulle (CDG) - Dortmund Airport (DTM).
There is no direct flight on the route from Paris to Dortmund
The shortest flights with change last about 3h 50min.