Square boxes instead of math symbols

[jj17720017]

Is there a way to fix this problem so that the proper math symbols are displayed? I'm reading a pdf that I obtained online. I've read the file before with Adobe Acrobat Reader DC without any problems, but this time many of the most common math symbols have been replaced with blank, square boxes. I reinstalled Adobe Acrobat Reader DC, downloaded any/all updates, and even re-downloaded the pdf. I've only had this problem recently, in previous months the file displayed just fine. It currently displays normally in Windows Edge as well as Adobe Digital Editions. I'm not sure if a recent update to Adobe Acrobat Reader DC is causing the problem, or if it can be fixed. The pdf file in question can be downloaded for free from:

https://descanso.jpl.nasa.gov/SciTechBook/series1/Goebel__cmprsd_opt.pdf

Or you can do a google search for it by looking for "goebel katz jpl"

[ptswilson]

If you open the file using pdf element 6 pro it will display and print correctly.  But when you save it and reopen it Adobe Acrobat reader, it will revert to the boxes.

[ptswilson]

Another thought.  If you use Wondershare PDFElement or something similar to get the file to display correctly, you can the use any of the 'print to pdf' packages (e.g. Microsoft or Bullzip) to 'print' it as a file, and is should then open and display OK with Adobe Reader.  That way you can preserve a correct version for the future.