As of 10th October 2017 Microsoft officially ended Office support for Mac 2011, which in short means that there will no longer be any new security updates, non-security updates, free or paid assisted support options or technical content updates.
It is advised that office packs are upgraded in order to keep your device and files safe as without security updates you may expose your device to various threats and it may not be compatible with future OS upgrades.
Office 2011 versions of Word, Excel, PowerPoint, Outlook and Lync have not been tested on macOS 10.13 High Sierra, therefore no formal support for this configuration will be provided. However, Office 2016 is fully supported on macOS High Sierra.
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