How can I set default pdf reader?

first of all, I switched back to EN9 since EN20 is crashing when I open pdf files in the reader window.

I deinstalled my pdf editor and installed a new one. Now the option “open with default program” is no longer available (EN9 and EN20), In my Win10 setting, the new pdf editor ist set as default program for handling pdf files.

Thanks for your time

JK