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Launch Microsoft PowerPoint. In the “Recent” list of files displayed in the opening screen, locate the document that’s giving you problems.
Find your PPTX file in the saved drafts folder when it opens. Open the file version you want from the list of AutoRecover saves.
Related Reading: How to Recover a Corrupt RTF File
Verify that your document contains the slides and graphics you expect based on your most recent edits. Click on the “File” tab and choose “Save As” to save your document under a new name.
For more detailed information read this article: https://social.technet.microsoft.com/Forums/en-US/50c99db5-9167-44fe-b625-e2682fa682ca/corrupt-powerpoint-file?forum=officeitprolegacy