Documents play a central role for many organizational processes. Current conceptualizations of documents predominantly engage with documents in two different ways. One sees documents as things with specific properties, and a second sees documents as medium enabling communication across different groups of actors. What is currently not well understood is how documents are perceived either as thing or as medium. This chapter engages with this issue by drawing from Fritz Heider’s epistemology of thing and medium, a concept stemming from social and media theory. According to Heider things are uniform and medium are multiform. Applying this concept to documents we argue that documents as things are perceived as uniform, whereas documents as medium are perceived as multiform. We exemplify the application of this conception of documents in the context of Gantt charts and the concept of boundary objects.