Why is that search process eating my CPU?

This post advised that with Adobe Reader 8, a new Adobe provider iFilter came to be.

That’s great, but I noticed that the windows desktop search was now using all my CPU.  Using process monitor, I realised the search was indexing pdf books that I had.

Granted it was low priority, but still was a small concern as to why it took so much CPU.

I wonder if its indexing the same thing twice?