MS Powerpoint does not show up identical on Preview or in iOS

We have files created on Microsoft PowerPoint (97 I think) (MS PPT). When I view these (default on Mac OS) in Preview App, the right and bottom 20-25% is cropped away. They do NOT look identical to when viewed on PowerPoint on PC, I have yet to try on MS PowerPoint for Mac. I have also not tried on Keynote, but these files are placed on a website:

http://godandsciencecollide.org/lessons/

and are meant for general consumption and viewing. I am a little disturbed to see that Preview application on Mac does not show them correctly and Mac users will be cropped inappropriately. Any suggestions? Is this a font size/type issue? Is there a way we can modify/save/export the PowerPoint files to view correctly on Preview application on Mac OS? (but also on PC/kindle/mobile devices etc.)

Similar viewing problems on iOS. On my iPad (and iPhone) screen when clicking on PowerPoint (PPT) files there is cropping of right side and bottom edge INAPPROPRIATELY. If you go back to view on MS PowerPoint the files are not cropped. (See Lesson 2 file http://godandsciencecollide.org/wp-content/uploads/2014/07/Power-Point-2.ppt) Suggestions? These problems seem identical between iOS devices but may be slightly different crop on Mac OS...

We want these files to look good on every device, so is this just Apple being sloppy about Preview software (I highly doubt!!) or is there anything that can be done about this? I assume printing would maintain the inappropriate cropping... Also a problem as these files may be printed for use in a sunday school class...

I DO NOT want to have to save different versions for each OS-device-brand combo of which there are WAY TOO MANY! (PC/Mac/Kindle/Android/iPhone/iPad/MacOS/Retina/non-Retina/Galaxy/etc.)

HELP!

FYI using MacBookAir 11"/iPad Air/iPhone 5