I've had this issue with PDF creator for a while now. I've been using this app since version 1.~ and I'm currently updated to the current version, still have this issue.
For example, this:
Turns into this:
And another example, the lines here are perfectly straight and not blurry before printing:
I've increased the DPI to 1200 and still no changes. Any recommendations would be great. This seems to only happen near areas where I have left comments, and as you can see in the first example, not all comments/lines are affected.