Unusually, on 1 December 1928 Friedrich Lütge was awarded a second doctorate. This time his dissertation concerned the history of the book trade in Jena, including the impact of the invention of printing. The work was supervised by Georg Menz. While working on this doctorate he was also employed in Jena as a private researcher by the economist-statistician Ludwig Elster. Projects on which he worked with Elster included the fourth edition of the Wörterbuch der Volkswirtschaftslehre ("Lexicon of Applied Economics") and the Jahrbücher für Nationalökonomie und Statistik ("Yearbooks of National Economy and Statistics").Erich Maschke: Friedrich Lütge [Nachruf]. In: Historische Zeitschrift. vol. 208 (1969), section 3, pp. 772–774 He also authored a celebratory booklet in respect of the fiftieth anniversary of the Gustav Fischer Verlag (publishing house): research for this commission supported and influenced the doctorate on which he was working at the same time. In 1929 he obtained a permanent position with Fischer as a literary editor and academic researcher. At Fischer he was entrusted with producing a number of works, mostly concerned with Applied economics (Volkswirtschaft) and Economic History
