It is unlikely to have been uninstalled without an explicit action by you but installing a viewer may have changed the file association which sets the application which is used when you double-click a file to open it.

First step is to do a search for the application. If you press the Window key and type "Word", does the application appear in the list of Apps? If not, open Windows File Explorer and do a search on C:\ drive for "winword.exe"

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Andrew Lockton
Chrysalis Design, Melbourne Australia