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If you have opened up a text document to see that work you had done in it is now missing, follow the steps below to see if it can be recovered through AutoRecovery. This is not a guaranteed resolution, and ensuring that AutoSave is enabled whenever possible is the best option for the future. You can turn on AutoSave by click the on switch up in the top right.
An older version of the document (i.e. one before any text was lost or deleted) may be saved in the AutoRecovery folder. To access the AutoRecovery folder, go to:
Finder > Go > Go to Folder... > ~/Library/Containers/com.microsoft.Word/Data/Library/Preferences/AutoRecovery.
You should see the older version of the document with the unsaved text in the Auto Recovery Folder, but won't be able to open it in Word. You should be able to open it in TextEdit, and then copy and paste the text into a new Word document. This most likely won't recover all text, but will recover a majority of it if you have done a lot of work in the document without hitting save.