The Pulp magazine industry...

Mitty works for a large publishing company devoted to the kind of pulp magazines that were popular in the 1920s and '30s. I doubt that these kinds of magazines were still as popular in the postwar era, as depicted in the film. With the exception of certain science fiction magazines, the pulp magazine industry faded after the war, replaced largely by the increase in comic book publishing. EC Comics replaced "Weird Tales" in the affections of the public.

Also, I doubt that a pulp magazine company would have had such well-dressed employees and such large, gleaming offices. I imagine their actual workplaces and the clothes they wore were much shabbier. I also doubt they could have afforded such elaborate photo shoots as inspirations for their lurid covers. As I recall, the artists of these covers relied chiefly on their imaginations.

Was the company in the film inspired by an actual company? Somehow I doubt it.