Attach files to elements in a stream c# API

Hello everyone!

I would like to prototype a workflow to programmatically attach to each element in a stream the corresponding drawing (or other file) existing in a local folder (via C# API) and having these accessible through the viewer.

Any good point to start from / resource I can look at?

Many thanks

Files uploaded to Speckle storage or navigable URLs to an external store?

It could be external for now, external local folders, using the element name or attribute value to pick the corresponding PDF file for example. Eventually uploaded content in a second stage.