Having had nothing but problems trying to install necessary dependencies for pycairo and other flavors of cairo, I considered what you said about the fonts being saved as stroked glyphs. That's it. I used a downloaded obscure font that no system is likely to have installed and then uploaded the resulting PDF to several mobile devices. The font showed beautifully and was fully scalable. So no need for embedded fonts. Problem eliminated.
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Here's the PDF.
Here's the PDF.