Weird distortion problem

I was an engineer on the Apollo moon program and my retirement hobby has been giving presentations to grade-school children.  Using the full Acrobat, I created a pdf to use for visual aids.  The schools use Adobe Reader to display the pdf.  There is one weird problem that has popped up occasionally.  Unfortunately, I discover it when I'm about to begin my presentation to the kids so I have no time for troubleshooting.

Most schools use "smart boards" and the problem does not occur there.  Some schools connect a computer to a projector and that's where the problem occasionally happens.  Looking at the computer screen, all is good (all images are perfect).  However, the projected images are stretched horizontally.  I can actually look at both simultaneously and the computer screen is good while the projected image is distorted!  The circular Apollo-11 shoulder patch appears oval, all persons appear fat, etc., etc.  Yes, the distortion shows up with all pages in the pdf.  This only happens with Windows computers.  In fact, in one instance, the teacher quickly swapped the Windows laptop for a MacBook (with the same projector) and the projected images looked good.

Any clues here, guys?  Please type slowly so that I understand - I'm very illiterate regarding Windows.  The only computers that I've ever owned have been Apple, starting with the Apple-II and graduating to the Mac.