Hi Maxim,
Thanks for your note.
I have an iMac, but I am running AutoCAD 2018 on a Windows 7 Professional
platform.. [Actually I have the Mac version of AutoCAD LT installed also,
but I've not worked on this particular .dwg file from the Mac side].

*An important note. *I partitioned my hard drive, which allows both Mac OS
X and Windows 7 to reside in my hard drive.
Attached is a screenshot showing computer hardware info.

I received a note from Autodesk a few days ago acknowledging that pdf
insert features are not the greatest, and that their IT staff is working to
improve AutoCAD.