The requirement for co-authoring in Office documents are:
- The documents need to be stored in a shared storage area that enables co-authoring (SharePoint Online, SharePoint Server 2019 and OneDrive).
- The documents need to be edited in applications that support co-authoring:
- Word: On all devices and versions more recent than Office 2010
- PowerPoint: On all devices and versions more recent than Office 2010
- Excel: In the the web browser version of Excel and in the latest desktop version of Excel for Microsoft 365
- The documents need to be of these file formats:
- Word: .docx
- PowerPoint: .pptx
- Excel: .xlsx
- All editors need to have edit-permissions on the documents.
- The documents must not be checked out, encrypted, marked as final or contain ActiveX controls.
The recommended maximum number of concurrent editors per document is 10. However, the limit is 99 and when this number is exceeded, each subsequent user sees a “File in use” error and can only open a read-only copy of the document. Having more than 10 co-editors will lead to a gradually deteriorating user experience with more conflicts, and users may need to go through more iterations to successfully upload their changes to the server.
Co-editing In Excel can sometimes be a bit complicated, for example when a user filters on a column, it will also impact the other users, so easiest is of course to work in different tabs and possibly communicate with each other and agree on which parts you work in.