In an earlier tip, I talked about how to remove all comments from a sheet. But that works on a sheet. If you want to remove from all sheets in one go rather than doing for every sheet separately, use following trick –
1. Office Button > Prepare > Inspect Document
2. A warning message will come, press Yes.
3. In the next box which comes, DESELECT all box except Comments and Annotations. Press Inspect.
4. If comments are found, it will say so. Press Remove All. This will remove All comments from the Workbook.