The IWorkbookIO.Origin handle the operation actually used — the file read, or the file written: the workbook's own origin for a plain save, a new one for a save that resolved a destination (a first save, a Save As), the target for an export. Its format is the one read or written.
The workbook that was read or written. A listener filters on this to react to a specific workbook (the service is shared across all of them).
Fired after a workbook has been successfully read.