OS X :: Large PDFs Slow In Preview

I seem to be having trouble with large PDFs in OSX. Everytime I open such a PDF file, either under Preview or Adobe Reader, ATSserver and mdworker begin taking up 60-80% of the CPU. Can someone please shed some light into what is happening? I understand that OSX is indexing the PDF file, but it indexes it everytime the PDF is launched, instead of just once. For example, I open Textbook.pdf (50mb) in Preview. As soon as it opens, the above two processes take up 60-80% of the cpu and seemingly dont stop. I wait, and wait, and eventually they do. So then I search for a word in the PDF file, and those processes start up again, searching becomes painfully slow as each instance of the term is searched for (I thought it indexed it). Once the searching for one term is done, and I decide to search for another, the two processes come on again, and everything slows down again. If I close Textbook.pdf and open it again either immediately or at a later date, the same things happen again.

Isnt it supposed to index once, and then be indexed forever? Instead of indexing everytime the pdf is launched, and everytime a term is searched for? This has made large PDFs almost unusable in OSX, unlike in Windows which doesnt seem to have this problem. Is there a solution?