Under the "Reservierung" column in the PDF, does it say anything about Sitzplätze? IME, most first class tickets nowadays come automatically with seat reservations, which would read something like "2 Sitzplätze, Wg. 29, Pl. 41 42, 2 Fenster, Tisch", which indicates you have seats 41 and 42 in car 29.

If your tickets don't indicate anything along those lines, you can reserve seats for €4 each on the website, or just get on the train and find seats that aren't marked as reserved.