The documents can be sent to the repository by different channels depending on their source and format. In some cases, such as the documents from TDX, collection is automatic and human intervention is not required to synchronize the two repositories. Other channels are the result of internal processes. For example, end-of-degree projects, bachelor's degree theses and master's degree theses are collected and sent by the tutors. And scientific papers are sent by a specific tool called Vertex, designed to add documents simultaneously to various repositories and programs.
More information: guide of the institutional repository.