pdf to tiff (600dpi and 300dpi) why there is a difference?

[knicks49]

Where trying to use "Save As > TIFF"  or "Save As Other > Image > TIFF" from Acrobat Pro (XI or DC 2017) image create are different, depending on the dpi settings.

I am trying to save to a image file in 300 dpi, but the text seems to be "filled" but when I try 600 dpi and text are okay. Can somebody point me to the right direction how to save to image on 300 dpi without ruining the text (I want to get the same view on the exported image on 300 dpi)

side by side comparison of exported image and save as settings