You may need to send them some sample files with older settings that still support the press standard, and maybe some set to non-press standards and see what they can open correctly. Yes, do ask them what version of Acrobat Reader, or Acrobat Pro, or acrobat CC they are running.
There are quite a few settings you can choose when exporting a PDF. You should find out what version of Acrobat Reader they are using to open the files and you might need to adjust your settings. Also, using transparency and then exporting to PDF can sometimes make for problems.
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