Your line should work but the space after c:\Program is causing it to fail. It shouldnt do that because you did escape the space with quotes. It seems like you found a bug. I'll fix it for the next update.
1 | RUN ACTION | | | | RUN VIA CMD /C | c:\progra~2\adobe\acroba~1\reader\acrord32.exe E:\File_John\F_variable\john.pdf
For now the line above works because I don't use quotes to escape the space. Instead I use a cmd line trick that trunks the full path. progra~2 is "C:\Program Files (x86)" because progra~1 on my system is "C:\Program Files". acroba~1 is "Acrobat Reader DC".
Thanks again John. I'll add that to the patch list.
Doing some more digging on this one. It looks like the problem is not with the internal white space in the MMM syntax but with our call command from the command line. 1 | RUN ACTION | | | | RUN VIA CMD /C | start "C:\Program Files (x86)\Adobe\Acrobat Reader DC\Reader\AcroRd32.exe" "E:\File_John\F_variable\john.pdf" works just fine.