Drag the LW doc to the icon of StuffIt Expander. Keep an alias on your desktop for convenience. Go to your File Exchange control panel and make sure that .sit is there. If not add it.

Sometimes the file is not really corrupt, but Expander gives you an error message and unpacks the doc anyway. Other times, it really is corrupt. There is a lot of garbage out there. Check the file sizes in the search window and you will see quite a variety for identical programs.