Since the January update of Acrobat/Reader DC a lot of users get this strange dialog when they open a PDF:
This is only useful for people who are using assistive technologies (e.g. a screen reader). The annoying feature can be turn off in Preferences > General… > Accessibility by deactivating the option Enable assisive technology support. This must also be repeated in the Reader preferences to avoid that this dialog is shown when a PDF is displayed in an Internet browser.