Nothing should happen to your existing word documents, except for the short period between removal and re-install the icon on them will go from the Word icon to a default icon, as the associated program (Microsoft Word) has been removed from your system.
As long as you don't have them all stored in C:\Program Files\Office or C:\Program Files\Microsoft Office, you should be fine. Which, by default, they should not be there anyway. They should be located in your MyDocuments folder.
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