A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
Start with a test that tells you whether the fault is in the sign in or in the file. One user in this thread fixed this exact error by signing in through the Share button, so check that first. Open the presentation in PowerPoint on your iPad. Tap Share. If PowerPoint asks you to sign in, sign in with your Microsoft account and try the export again.
If it still fails, test with a new blank presentation. Make one slide with a short title only. Try to export that file to PDF. If the blank file exports but your file does not, the fault is in your file, not in the app.
For a file that will not export, save a copy to OneDrive first. Then open that copy in PowerPoint for the web and export it to PDF from there. If the web export works, you have your PDF and you know the iPad app is the problem.
Also check two simple things before you reinstall anything. Make sure PowerPoint is updated from the App Store. Make sure your iPad has free space for the PDF. If the file has very large videos or pictures, try a copy with those removed, just as a test, to see if size is the cause.
Tell us which test fails. The blank file test and the web export test point to the right fix.
This answer was prepared with help from Muse.
Microsoft reference: Save your presentation: https://support.microsoft.com/en-us/office/save-your-presentation-0a0c4a6e-269b-4ffc-b573-9dea5d7f52b2