If you find that you cannot Co-edit a document, it has been locked for one of the following reasons:
- It has been been approved or complete in Workflow.
- It is currently being edited by another user.
- It has been sent to the client for signature or is signed by the client.
'Legacy documents' (that is, from old versions of Office such as .doc or .xls) cannot be Co-edited. Export the file, save it as the latest Office version (.docx, .xlsx), import it to FYI and you will then be able to Co-edit it.