Be careful with sending PowerPoint presentations that could have left overs of confidential information hidden inside that you do not want outsiders to see:

• Comments in the speaker notes field at the bottom of the slides ("Let's don't tell our investors yet, about the disappointing Q1 results, we will do that in 2 weeks"). When you use an old presentation to "copy-save" it as the master of a new one, comments get copied across as well. 
• Regular comments on slides that have not been removed
• Information, comments, analysis, that sits in the Excel engine of data charts, when someone clicks "edit data", the full Excel sheet opens
• Also, even if you remove the data labels or axes from a data chart, the data still remains visible when hovering over it with a mouse.

It is best to share your presentation as a PDF file, but even then watch out with information that becomes visible when hovering over with your mouse (data points, file names of images, etc.)

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