Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Extract Image Files from MS PowerPoint and Word 2007 Documents
To get all graphics from a .pptx or .docx file with several clicks:
1. Download Stuffit Expander or Stuffit Deluxe.
2. Drag a file onto the app.
3. Find all images in the media folder.
Note: The above steps work only for Office 2007 documents, as they are xml-based and therefore can be expanded by Stuffit as a folder.