The easy solution is to convert PowerPoint files to PDF. If you want to stick to the PowerPoint format, here are some things to watch out for:
- Data charts (bars, pies, columns) in PowerPoint are generated via an embedded Excel spreadsheet. Even if you did not include data in the graph, the source still sits in the Exel file. Open the spread sheet behind each chart and check whether it contains redundant data you do not want to disclose. (For example breakdowns by category, or in case of public investor presentations, forecast of financials beyond the current reporting period).
- Cropped pictures that were not compressed still remain in PowerPoint in their full size, if you reset the image it comes back in its original form. If you do not want that, select the image, then compress, then ask PowerPoint to remove the cropped areas of the image.
- Hidden content such as author information, speaker notes with informal side comments such as ("not sure whether this is true, I made it up for the moment"), or objects that are outside the canvas of the slide. In PowerPoint 2010 you can inspect your presentation for things like this in file, info, prepare for sharing.
P.S. Image tags can be an unwanted piece of information in PDFs, here is how to get rid of them.