title_body: Hide a folder of ebooks on Kindle
upvoted_answer: Well, it's a bit of an involved solution, but you could access the "documents" folder on your kindle via miniUSB/USB data and charging cable with your computer, and compress the book (and remove the original). Kindle will not recognize the file anymore, though it still contains the same data. 
  
  NOTE, however, that if the file in question has a duplicate in the cloud, the duplicate will remain accessible.
  
  For this purpose, I recommend Settings>Device Options>Parental Controls>Restrictions>Cloud (and an adequate password). 
  
  You may also want to restrict access to the Kindle Store? Just sayin'.
  
  These steps will secure the files on your kindle, but inaccessible by kindle;
  in your kindle cloud, but restricted to those with the password.
  
  (Just tested on my Kindle 7th Gen.)