Co-authoring in Microsoft Office apps

Co-authoring with CDM is turned on by default, but some scenarios may block or prevent collaboration with others. The following situations can cause issues when attempting to co-author Microsoft Office documents:

  • You or somebody else has checked out the file. If your organization requires you to check out files, it can prevent other users from collaborating on documents with you.

  • A user has encrypted the file using password protection.

  • Your administrator has turned off co-authoring with CDM. For more information, see Turning co-authoring off or on.

  • CDM does not support co-authoring for the file format. For more information about supported file formats, see Co-authoring with Cloud Drive Mapper (CDM).

  • You or somebody else has marked the file as final, making it read-only.

  • The file size exceeds the supported limit. Files over 50MB will result in an inconsistent co-authoring experience.

  • The file path, including the file name, must not exceed 256 characters for OneDrive or SharePoint in Microsoft 365. If you exceed the limit, co-authoring will be automatically turned off.

  • You or somebody else left the document open for an extended period without closing it.

  • Co-authoring is not possible if you create a new file and save it while CDM is paused or offline.

  • Co-authoring is not possible if you create a new file and do not save it to a mapped drive.

  • CDM.CoAuthHandler.exe is not registering correctly during installation or upgrade. For more information about the registration process, see Checking the CDM.CoAuthHandler.exe process.

  • The document is protected using Information Rights Management (IRM) or Digital Rights Management (DRM) without Sensitivity labels. To collaborate on documents with IRM protection using Microsoft Purview Information Protection Sensitivity labels, you will need to ask your administrator to enable co-authoring for encrypted documents in Microsoft Office.

  • Certain Office Group Policy settings prevent co-authoring, including Disable Automerge Client Policy, Disable Co-Authoring Server Policy, and Disable Co-Authoring Client Policy.

  • The file is an Excel or Word file containing ActiveX controls.

  • You are attempting to collaborate on an Excel workbook that utilizes the ISO strict version of the Excel Workbook file format (.xlsx).

  • The Excel or Word file contains an unsupported object, such as an Object Linking and Embedding (OLE), SmartArt graphic, chart, or Ink object.

  • You are using a Word document that uses master documents with subdocuments, contains HTML framesets, or is being published as a blog.

  • Up to 10 users can collaborate on a document simultaneously without any issues. The upper limit for co-authoring is 99 users. However, you should expect issues while co-authoring a document with more than 10 users at any given time.