Missing fonts Ariel and Helvetica reported on PDF load, but they are present

Adobe Illustrator CC 23.0.1 (64-bit)

When I load a PDF drawing generated by a CAD program, I am consistently given this error message, and all of my imported text is highlighted in pink, presumably to show the font mismatch. Of course these fonts are actually present in Windows 10.  I try to Find Fonts, but even when I point to them, they won't load; maybe I am doing that wrong. The substitute font is a different width, and is misaligned with virtually all of the graphics, making many features unreadable. If I select each bit of text individually and reassign Arial font, they look fine again.  But the Find Font mechanism is supposed to take care of that, right?

I have read similar questions, but it looks like they don't have answers, or those answers don't seem to work. 

• Windows 10 64 bit
• Two different machines yield identical results