Microsoft Word "Save as PDF" - fonts not rendering

One thing I'd also check is whether Word is treating the different weights as separate font files or just as style variants within the same family. I've run into similar behavior with a few open-source variable fonts where the document looked perfect in Word, but the built-in PDF export flattened everything to a single weight, while Print to PDF preserved the appearance.

If you're using the variable version of Readex Pro, it may be worth testing with the static font files (Light, SemiBold, etc.) instead of the variable font, just to see if the PDF export behaves differently. If that fixes it, it would point more toward a limitation or bug in Word's PDF export engine rather than a problem with the font itself.

Also, after creating the PDF, open it in Acrobat and check File → Properties → Fonts to verify which font variants were actually embedded. That can help determine whether the wrong font is being embedded or whether the PDF viewer is substituting it during rendering.