I can (usually) get into Annotation mode on Evernote for iOS 10.1 by opening the note and tapping the Edit button , but actually annotating PDFs seems to be mostly broken. Ever since v10, problems abound. I pay for Evernote Premium despite having OneNote as part of my O365 subscription because Evernote is (has been in the past) a superior product. If these issues continue much longer, I will have to abandon Evernote for good. I really don't want to do that.