I have a Powerpoint pptx presentation which reports and error when I attempt to open it. The system may have been turned off in the middle of a PowerPoint session

What is good software for PowerPoint file recovery?

Have you tried the built in file repair process.  It is an option when you use the file open dialogue box, there should be a drop down on the Open button that has Open and Repair

Or

PowerPoint Repair Toolbox is efficient PPTX corrupted repair solution for damaged presentations in corresponding format so you may open these documents anytime and regardless the reason of file damage.

For more: https://www.pptxrepairtoolbox.com/

• Marked as answer by KennethHubb 17 hours 52 minutes ago

Have you tried the built in file repair process.  It is an option when you use the file open dialogue box, there should be a drop down on the Open button that has Open and Repair

Or

PowerPoint Repair Toolbox is efficient PPTX corrupted repair solution for damaged presentations in corresponding format so you may open these documents anytime and regardless the reason of file damage.

For more: https://www.pptxrepairtoolbox.com/

• Marked as answer by KennethHubb Saturday, August 29, 2015 1:38 PM