My guess is that it was turned into a PDF directly from a TeX DVI file with bitmap fonts rather than compiled directly into a PDF using outline fonts with pdfla

My guess is that it was turned into a PDF directly from a TeX DVI file with bitmap fonts rather than compiled directly into a PDF using outline fonts with pdflatex. Some people are just used to using their existing document processing pipelines rather than using more modern tools like pdflatex, I guess. Edit: the file predates pdftex. Back then, the file would've just been sent to a printer rather than rendered on screen for anything other than a preview, and it looks fine when rendered. If it was passed through pdflatex these days, it'd look much better.