The presentation will open in Google Slides but remain a PowerPoint file as you can see next to the name on the top left. Click "File" and "Save" as Google Slide from the menu to convert it.

Turn PowerPoint slides into image files to use in other apps From the File menu, choose Save As. In PowerPoint 2007, click the Office button and choose Save As.

Offline work with Google Docs, Sheets and Slides in either Chrome or Microsoft Edge gets easier for Word, Excel and PowerPoint format files.