This doesn’t happen to us all the time, but sometimes after importing a PDF drawing into AutoCAD there are lines connecting objects that shouldn’t be there. The lines didn’t show in other programs. This turned out to be a simple setting in our AutoCAD. We needed to turn off “linesmoothing”. Here is the article we used to fix our issue.

In AutoCAD go down to the command line and type in “linesmoothing” and hit enter. Next type in “off” and hit enter. Import the PDF again and the lines should be gone.

https://knowledge.autodesk.com/support/autocad/troubleshooting/caas/sfdcarticles/sfdcarticles/Unwanted-linework-appears-when-opening-drawings-in-AutoCAD-2015.html

Let us know if this helped you.