This article compares the definitions of the document, produced by the document theorists and the arguments advanced by the French historical epistemology of the twentieth century in order to set what is a reliable documentary source. In the context of digital post-truth, the former criteria, based on the paradigm of truth and authenticity guaranteed by institutions and scientists, can be questioned. We suggest to consider the production of historical narratives as a design process, and to evaluate the truthfulness of a source according to their three regimes of documentality: textualization, auctorialisation and documentarisation.