I have configure SharePoint Online successfully as my external document management and file storage system using the standard Files Connect adapter.

Now I want to attach a file that is stored in SharePoint to a Salesforce Record, in APEX code. However I was not able to figure out how this might be possible. Anyone succeeded in doing this? I would also go for creating a Chatter post in APEX, but the FilesCapabilities do only support linkage to existing ContentDocument record, but my SharePoint files are not (yet) listet there.