I speak and read German, and the translation is substantially correct. I say "substantially" only because I'm pretty rusty. I see no glaring errors. The letter is signed by an engineer from Hirtenberger. Below the signature, you'll see "Ing. Goluch Karl-Heinz." The "Ing." is short for "Ingenieur" (if I've spelled it right), which means "engineer" in German. Given the spelling, I believe that it's been adopted into German from French.
ETA: As far as the translation on the kinds of ammo used (the block of text in the middle with numbers), I can't really vouch for that, because I don't know what the abbreviations mean, like VRMK, for example.
I'm a lawyer, but I'm not your lawyer. If you need some honest-to-goodness legal advice, go buy some.