ηὕρηκα! I think I solved this PDF problem well enough for my purposes. The key is PDF/X, a family of subsets of PDF meant for, as far as I can tell, actually doing what PDF is supposed to do, i.e. unambiguously describing a document.
So if you ever find yourself with an existing PDF file that doesn't have base 14 fonts embedded, and you don't have access to the PS or whatever that generated that PDF, and a round-trip through pdf2ps and ps2pdf rasterizes all the fonts and makes them look hideous, do this instead: