It occurred to me to directly compare a PDF I made with AbcExplorer some time ago, with exactly the same PDF printed again today, on the same paper, with the same Canon printer.
Under the magnifying glass it was obvious that the new print was much less crisp and much more splattery.
And then I remembered that the last time I renewed my black ink cartridge I bought a "Cartridgepoint" "OWN" brand instead of a Canon, (for the first and last time) figuring that as the print head is part of the machine and not part of the cartridge, the line would be the same. But the ink has spread away from where it was applied, producing a less clear edge.
I tried the same with ABC2Win, which I know normally produces very clear print, and the result was the same blurriness, no better than AbcExplorer. So the problem is the ink.
I now know why the Canon product costs almost twice as much.