The solution here is to use Adobe Reader to open the file. Note that even if they don't want to pay for Acrobat, they can still download Adobe Reader for free from the Adobe website. I'm not entirely sure what you or your customer mean by " it no longer supports earlier versions of Adobe Reader," but the most recent version of Adobe Reader
Close any browser that is displaying a PDF. Go to the Adobe Acrobat Reader download page and click Download Acrobat Reader. When the Opening dialog box appears, click Save File. Press Ctrl+J to open the download Library. When the download Library window appears, double-click the .exe file for Reader. If prompted to open the executable file Despite what anyone may tell you, a normal user will not see way to install Adobe Acrobat Reader DC without getting unwanted McAfee software installed. Yes, it can be uninstalled afterwards. It is still scammy behaviour. Yes, I have mentioned this on the adobe forums. qIQD.