A forced cumulative update also reset PDF viewing to Edge on many PCs.
Right click, chose Adobe.
But someone who knows this stuff better than me switched me back to IE. I hope I can keep it.
There are numerous reports of this update failing to install, entirely. My Window 10 test machine is one of them - it has failed to complete this update 6 times so far.
Just a personal opinion (albeit shared by many) but IE is not a recommended choice.
YMMV.