To show yourself a newspaper or book in the mirror, you reorient it so its backside faces you. The mirror is not reversing left and right but is instead showing you what the front side would look like if you could view it from the back.
If you wrote a word on translucent paper and then held it up in front of you to read through the paper, you would see it backwards, exactly as you see it in the mirror. You wouldn't see it upside down. I'm not very good at explaining, but you might make something of my attempt.
To show yourself a newspaper or book in the mirror, you reorient it so its backside faces you. The mirror is not reversing left and right but is instead showing you what the front side would look like if you could view it from the back.