Cedaronbelay
i'm assuming this is in your main profile? i would start by going to settings -> apps -> see all apps and checking to confirm PDF Viewer is listed there and does not say disabled.
sidenote, what launcher do you use? it may play a role.
Cedaronbelay come on dude, you're the one with attitude here. op clearly describes that the system says it's installed but cannot access it. what does sending them to the one paragraph blurb do to help them?