In apstrata, a File is any digital content or asset that gets attached to a Document. More than one File can be attached to a single Document, or even to a single field within a single Document. One of the Document fields can be a File, with associated read and write ACLs.
Hence, a developer can easily upload or download Files as part of the developed application.
For more specific details, please check the SaveDocument API for uploading files or the GetFile API for downloading files.