Looking at screenshot, you can see that the same pdf looks much more edgy in Okular. In addition, even though both Evince and Okular have image zoomed at 400%, actual text sizes are different, and okular shows the larger text. Not sure who is right. But if to display the text with regards to the same actual screen resolution, only one size can be right.
Created attachment 70277 [details] screenshot of comparison to evince
Created attachment 70278 [details] pdf sample page
Actually, I made a mistake. Okular shows the smaller text, Evince shows larger one, and Acrobat shows the same even larger at the same 400% zoom. Two of them or all of them must be wrong. Evince shows the best rendering quality compared to two others.
This is an upstream (poppler) issue. Please report the bug at https://bugs.freedesktop.org/
The problem with reporting this upstream to poppler is that evince is also using poppler (http://en.wikipedia.org/wiki/Evince). So it must be something in the way how poppler is used, maybe some option, that triggers the rendering problem. Same with the scaling issue.
I'm the poppler maintainer, trust me.
same was reported upstream: https://bugs.freedesktop.org/show_bug.cgi?id=48513