With SharePoint, users can simultaneously edit the same document using the Office Web Apps or, in some cases, the desktop version of the software. Microsoft calls this co-authoring, and it has been a very popular feature.
Co-authoring was initially announced with SharePoint 2010, but was limited to Word, PowerPoint, Visio, and OneNote. SharePoint 2013 extends this functionality to Excel through Office Web App or Office Online.
Co-Authoring is not available for use with the desktop version of Excel.
Different products co-author differently
Not every Microsoft Office product co-authors in the same way. In Excel (through Office Web Apps) and OneNote, the cursor for each user and what each user is typing is immediately viewable to all users.
For example, if everyone opens a OneNote document during a meeting, they can all type at once like it is a virtual whiteboard.
Word and PowerPoint files only upload changes when the document is saved. Users know that someone is co-authoring, but the co-authors’ changes become viewable in big chunks with each save. To prevent version conflicts, any paragraphs being edited are locked down until changes are submitted.
Users co-authoring the same Word or PowerPoint file, should regularly save their document so that other users can see their changes.
Office 2007
Co-authoring requires Office 2010 or Office 2013. Office 2007 users cannot co-author. They can edit documents by checking them out and making changes, but if another user is coauthoring, their access to the document will be declined.
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Steven A Nichols 