tl;dr: WPS Office now has a presentation mode (as of May 15 2018)
Once upon a time, the iOS version of Microsoft PowerPoint has a presentation mode. Using an iPad with the lightning to VGA adaptor, you can show the presentation slides normally on the projector while showing slides with notes (and other things) on the iPad screen. But what Microsoft giveth Microsoft taketh, and at some point, after an uneventful "update," the feature was eliminated. Eliminated, perhaps, is not quite the right word. Rather, presentation mode has become a premium feature that requires an Office 360 subscription to use.
Alas, I did not realized the change until it was too late. In the olden days of iTunes and iPad syncing, it was possible to revert to the version that's stored on your computer -- an ipa file. Unfortunately, the older version of the ipa file with presentation mode was overwritten with a couple of newer versions. Since the lost, I have vowed to avoid updating iOS apps. But also, I have since been wandering the iOS app store wasteland to find an alternative.
On and off for years, I have checked updated versions of apps like Google Slides, Polaris Office, WPS office, and yes, even Microsoft PowerPoint. I've also download lesser known apps like Brainshark. And recently, finally, I find that WPS office has implemented a presentation mode!
So, if you are like me, and have been wandering the iOS wasteland looking for that one iOS app with presentation mode, go download it now! And then, never update that app again.