Large File 150 MB Crashes

Hard to say without seeing the PDF.

Make a copy of the PDF and try optimizing it, (File> Save as other> Optimized PDF), your PDF may have many unnecessary layers and complex vectors, optimizing it using the right settings (remove everything you don't need) may reduce the size and speed viewing. Are there really 5,000 comments in the file? I don't think they could be from the CAD software, if there are no comments, include the optimization option to "discard all comments" (first option, second panel of the attached screen shot with suggested optimization choices). Do you have the original CAD file and software? Try re-exporting it as a PDF.

Note the "Audit space usage" button at the top right corner of the optimizer panel, clicking this may give you some clues about the size.