Complex sentence: His subisidiary task was to secretly obtain informations on the French Army, whereby he became involved in the Dreyfus Affair: in 1894 he received an anonymous offer for the purchase of rather insignificant military intelligence, outlined in an unsigned "bordereau".
Split into simpler sentences: His subisidiary task was obtain secret informations on the French Army, and he became involved in the Dreyfus Affair. In 1894, he received an anonymous offer for the purchase of rather insignificant military intelligence, outlined in an unsigned "bordereau".