PurposeThis paper re-examines the ontology of documents, especially digital ones, in the context of preservation, which presumes the actual existence of things. It also explores which aspects of documents are retained or lost over the course of time.Design/methodology/approachThis study detangles the complexities of existential dependence relations of documents, by selectively reviewing literature on digital preservation, document theory, John Searle's social ontology, Maurizio Ferraris' documentality, and Amie Thomasson's categorial ontology.FindingsThe author argues that (1) existing objects can be documents, insofar as perceivers regard them as such; (2) documents are social objects as they depend on other objects, including creators, perceivers, and other documents; and (3) preserving digital documents entails the curation of dependence relations since they inherently have technologically dependent relations.Practical implicationsA clarification of the existential dependence relations of documents can aid documentary heritage institutions in determining preservation goals and strategies. Future research must address how, and to what extent, such dependence relations can be curated.Originality/valueThis paper clarifies that the preservation of documents entails the curation of dependence relations, and the critical issue in preservation is how to best preserve the dependence relations of documents, especially since digital documents available on the Internet inherently have technological and dynamic dependence relations.