Reviving a four year old unanswered question: Why is there a different font thickness if compiling differently?
This time providing the output pdf files:
Not only font thickness, but microtypography is also different. You'd be able to notice if you open both documents in "maximized" mode, and switch back and forth between the pdfs very quickly (e.g., with Alt-Tab or something similar, I'm using i3wm so it's very easy for me). As an example, in the second word 'ipsum', 'u' is closer to 's' in latex, but closer to 'm' in pdflatex.
How to fix this, i.e., have consistent look of the document?
Since I like the thicker text but use pdflatex for my work, how to reproduce the thicker text in pdflatex?
EDIT 1: So I noticed the thickness is not visible in google pdf viewer, but it's visible in both evince, and zathura pdf viewers. I haven't tested adobe acrobat though.