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Word Online and versions of desktop Word as far back as Word 2010 provide the ability for more than one person to edit a document at the same time (co-authoring). If you can’t co-author a document, one or more of the following reasons might be the cause:

  • The document is open in a version of the Word desktop application that doesn’t support co-authoring (such Word 2007 or earlier, or Word for Mac 2008 or earlier). If you want to co-author in the Word desktop application, use Word 2010 or later.

  • The document is stored on a server that does not support co-authoring. Store your document on OneDrive to take advantage of co-authoring in Word Online.

  • The file format is not supported. Only .docx documents can be co-authored in Word Online. When you click Edit in Browser, Word Online prompts you to convert a .doc file to the new format. Click Convert, and then click Edit. Be sure your co-authors work with the .docx document. You might want to append “backup” to the file name of the original document, which Word Online stores in the same folder as the .docx copy it creates.

  • The document is marked as final to prevent accidental changes. If you need to edit the document, open it in Word and turn off Mark as Final. (Click Open in Word. In Word 2007 click the Microsoft Office Button, point to Prepare, and then click Mark as Final. In Word 2010 and later click Edit Anyway in the Marked as Final bar across the top of the document. Save the document. If you opened it in Word 2007, close the document so that it can be edited in Word Online.)

  • The document contains an OLE object, or the body of the document contains an ActiveX control.

  • The document does not have the Store random numbers to improve Combine accuracy check box selected. (On the ribbon, click the File tab, click Options to display the Word Options dialog box, click Trust Center, click Trust Center Settings to display the Trust Center dialog box, click Privacy Options, and then under the Document-specific settings section, make sure the Store random numbers to improve Combine accuracy check box is selected.)

  • The document is a very large file size. For tips on reducing the file size of documents see Reduce the file size of a picture.

  • Certain Microsoft Office group policy settings prevent co-authoring, including Disable Automerge Client Policy and Disable Co-Authoring Client Policy.

  • The document uses master documents with subdocuments or contains HTML frame sets.

Note: In SharePoint 2010 and in SharePoint 2013 on-premises, Word Online is called Word Web App.

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