We have had a couple of reports of AutoCAD/AutoCAD LTon MAC (any version) locking up when printing or saving to PDF:
When the Mac locks up, you will need to force quit the application or wait for it to respond which will take forever.
To get around this issue and to avoid the Mac beach ball, you will need to remove the printer before you print or save out the PDF file.
Once you remove the printer, you can save to PDF 'instantly'. Just a note, not all printers are problematic but some will work as expected.
Thanks to Ben Simms for confirming that this solution worked.