I got tired of having Adobe Updater constantly running in the background (why not a scheduled task run periodically like Google Updater?!) and the need to update/reboot my PC regularly when a new version of Acrobat came out.
I switched PDF viewers briefly but ended in the same update cycles I was in with Adobe.
PDF.js isn't perfect but I've yet to come across a PDF that it couldn't open for me. I use it mainly to view things like insurance bills or other random documents where pixel perfect rendering is irrelevant.