She created the Librairie Droz, a publisher and seller of academic books, at Paris in 1924, moving the business to Geneva at the end of the war.

Between 1910 and 1913 she taught French at the Moravian Institute of Gnadenberg in Silesia, taking the opportunity at the same time to perfect her German.

She moved to Paris in 1916 and enrolled, at this stage as Eugénie Zahn, at the École pratique des hautes études (Section IV – Sciences historiques et philologiques (loosely, History and Philology).

[6] She described the Paris premises proudly in her first catalogue: "Accommodated in the House of the Bronze Horse, given by Francis I to [the renaissance poet] Clément Marot in 1539, the 'Librairie Droz' [book business] has been established by Eugénie Droz, graduate of the École pratique des hautes études and docteur ès lettres.

[7] Despite the Librairie Droz [fr] having been established in Paris, the printed device appearing as a form of trade mark on publications acknowledged the Swiss provenance of the proprietor.

[8] Shortly after opening the Librairie Droz, still aged only 32, she found time to take on a position as assistant treasurer of the Société des anciens textes français, a learned society founded in Paris in 1875 with the purpose of publishing all kinds of medieval documents written either in langue d'oïl or langue d'oc.

)[9] In 1934 she founded "Humanisme et Renaissance",[9] an academic journal which in effect replaced "Revue du seizième siècle".

In 1963, the year of her seventieth birthday, she sold the business, which passed to the control of Alain Dufour and Giovanni Busino, two young historians with complementary skills whom she had personally selected.