When using Ubuntu unity dashboard, all the recently accessed documents and items are shown by default.
To turn this off and also to make sure none of the upcoming documents or other items are visible in the dashboard :
1. First, go to System Tools > System Settings and then select Privacy.
2. Then in the “Recent Items” tab , select “All” for the “Forget activities” option and hit “Delete history”. Finally, at the bottom, turn the slider to “Off” for “Record Activity”.
From now on, none of the accessed files or documents will be listed when using the Ubuntu dashboard.
Cheers.