acrobat external window handler

I have installed Acrobat Reader DC a number of times but still get an error message "Could not find Acrobat External Window Handler " when  External window handler |Adobe Community.
When I try to download and open a PDF document I get an error msg that says " Could not find Acrobat external window handler. I have checked.
2 or more PDF files without closing the first open browser i get an Acrobat plug- in error "Could not find Acrobat External Window Handler ".

Acrobat external window handler - employers also

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