Ibooks

I have a problem with Ibooks in my Mac Air.

The app opens normally and books open normally - but after a while (5mins) of reading the whole thing gets stuck. Also my mac is very hot. When I checked which process is taking on such a toll on the processor, I noted that Ibooks take up over 100% of the running memory!

Does anybody have same sort of thing going on? What can I do?

My Ibooks seem to be version 1.12 and I have just updated to High sierra.