Some books are appearing pink in Preview.app

I recently copied some PDF books onto my MacBook Air (running macOS 10.12 Sierra). Almost 80 % of them appear to good. They are readable in Preview.app. They appear as they would have appeared on any other app. But some books are appearing totally pink. The background is totally pink. Even in the folder they appear pink. For clarity I am attaching the appropriate screenshots. I need help on how to solve this

Solution 1:

To solve the red/pink background follow these steps:

1. Open the existing PDF in Preview.app
2. Select File > Export as PDF...
3. Save the new PDF in a different location.

The new PDF will have no red/pink background anymore.