Krita is closer to a Photoshop competitor than Illustrator. Inkscape is like Illustrator but honestly it is not very good, mostly due to seriously poor performance.

I don't know if Atril is a good Acrobat Reader replacement either. Does it support PDF forms and annotation? That's what most PDF readers are missing.

Apple's preview is pretty great from that point of view. I've also used Xournal++ for that in the past.