The Windows 10 Start menu..
I must be honest. I don’t have a problem with it because I hardly ever use it. Start10 and Classic Shell give me the start menu that I like best while still giving me the option to use the default menu if I wish. I have yet to see either classic menu fail. Use one or the other, btw.. 🙂
Windows 10 has it’s own cute way of dealing with and offering help regarding PDFs, but again the older ways win out best.
I install and have installed Foxit Reader over the last four Microsoft operating systems, again without the issues that one might get with Adobe Reader or Windows 10. Strictly speaking, it should set itself up as the default PDF handler, but in case it doesn’t. go to Settings > System > Default Apps and set it there..