iBooks not show books in my ipad at moment synch

HI friends:

when synch the iPad with iTunes the place where are iBooks I can't synch my books both pdf, in my iPad are the pdf but in iTunes synch not!..

the questio is why?

how the save in my iTunes acocunt whe doing synch? And my device are with la the last update iTunes and IOS 3 days ago download the last version.

in my mac book air are the pdf in iBooks app of mac book air, but, again in iTunes synch not appear!..

Please your help ever efficient... i hope for that!!

ZIPAPPLE