Microsoft has announced in a support document that Office for Mac 2011 will not be supported under macOS 10.13 High Sierra. It doesn’t go as far as to say the software will not work, but hints at this.
Word, Excel, PowerPoint, Outlook and Lync have not been tested on macOS 10.13 High Sierra, and no formal support for this configuration will be provided.
It also notes that users of Office 2016 for Mac may experience problems with High Sierra …
Microsoft says that versions 15.34 and earlier are not supported, and you may not be able to launch the apps. You are advised to update to 15.35 or later, but even that’s no guarantee.
Not all Office functionality may be available, and you may encounter stability problems where apps unexpectedly quit. During the beta period for macOS 10.13 High Sierra, no formal support is available for this Office configuration.
We strongly recommend that you back up your existing data before trying the software. If you encounter issues using Office 2016 for Mac on High Sierra, please send us feedback so we can address them.
The company also advises that support for the 2011 suite ends next month – including security updates.
All applications in the Office for Mac 2011 suite are reaching end of support on October 10th, 2017. As a reminder, after that date there will be no new security updates, non-security updates, free or paid assisted support options or technical content updates.
MacWorld notes that Mac users of Microsoft Office get second-class service from the company, offered only five years of security updates instead of the ten years given to Windows users, alongside often long-delayed porting of new features.