Aha, looks like the PDF renderer is set by the latex_engine variable in _output.yml.
After changing that from the default of xelatex to pdflatex, PDF rendering seems to be working.
Sorry for the noise all. 
Aha, looks like the PDF renderer is set by the latex_engine variable in _output.yml.
After changing that from the default of xelatex to pdflatex, PDF rendering seems to be working.
Sorry for the noise all.