I tell the child that what she's doing is wrong, and ask her, politely but firmly, to give the book back. I then try to move my child away from the horrid child, if she doesn't start being nice.
Snatching is normal in a two-year-old, but not in a five-year-old (at least not without SNs).
My worst experience with this was at the local library. DS2 was maybe 15 months, and a 4 or 5-year-old girl decide she had to have all the toys, about 15 of them. She couldn't play with them, she had to just hoard them.
I explained that my DS2 would like a truck or tractor to play with, and asked her to give me one of them (didn't care which one). She sobbed, held onto all the toys, and refused to speak to me. I explained that I was going to count to five, and then take one of the tractors, if she didn't give one. She sobbed, and didn't give me one.
I counted, and gently but firmly took a tractor (she held on, sobbed, etc).
Then DS2 played with the tractor and this horrible child's mum consoled her for her trauma. The mum never said anything to me.
Poor little girl, she was in for a real shock when she started school.