First, the main way PDF readers make strokes thicker is via hinting, so it depends on how Computer Modern was embedded into the PDF for starters.
Second, hinting distorts letterforms so many top-quality renderers (like on macOS) don't use it, preferring more accurate letterforms instead. And Preview on macOS is certainly "decent".
Third, "updating" isn't going to do a thing. Whether fonts are rendered as hinted or not is a design decision taken when the PDF rendered was built from the ground up. No "update" is going to change that.
First, the main way PDF readers make strokes thicker is via hinting, so it depends on how Computer Modern was embedded into the PDF for starters.
Second, hinting distorts letterforms so many top-quality renderers (like on macOS) don't use it, preferring more accurate letterforms instead. And Preview on macOS is certainly "decent".
Third, "updating" isn't going to do a thing. Whether fonts are rendered as hinted or not is a design decision taken when the PDF rendered was built from the ground up. No "update" is going to change that.