Yes, it's another Bewitched item!
Now, I'm going purely by memory here, but in the 1960s, Golden Books produced a whole line of books like these, hardback novels based on various TV shows of the day... I remember seeing an Annette book at a swap meet not too long ago... I guess they were bigger books for readers (presumably pre-teens) who had outgrown Big Little Books!
What's interesting to note about this cover (and isn't that a groovy image there?) is that it features the second Darrin, Dick Sargent. That would help to date when this came out (to be honest, I always preferred Dick York's Darrin).