BIM360 Docs is a file management system, not a document management tool. A document is more a database entry with an ID, a title, description, code and other attributes and is a container for several files (native, PDF, appendix, control form).
An example is given below: a document is a database entry with metadata and files are associated to this database entry.
As a consequence, metadata are associated to a document, not a file. And a workflow is triggered against a document, not a file.
Your idea of sets is almost what we need, if we can send them in a workflow and if we’re able to create attributes against each set. Remains the fact that we’d also be happy to use sets for the purpose they’ve been designed for (a bid package, a handover dossier etc.), so I don’t know if we use sets for each « document », we’ll be able to use them to build other sets.
This request is a change of paradigm in the application and not sure can be met through this tool.