iBooks: how to sync PDF only?

I use my iPad as PDF reader, so my iPad contains many PDFs which I'd like to sync.

It should be the steps below:

1. You need to login with correct Apple ID on every device you want to sync
2. Plug in iPad/iPhone to your Mac (my situation)
3. Open iTunes
4. In iTunes go to File → Devices → Transfer purchases from <iOS device>.

But iTunes copy all my apps, not only books or PDFs.

Solution 1:

In Yosemite, this is now possible using only iBooks. On your iOS device (in my case an iPad 3rd Gen running iOS8), enable 'sync collections' in the settings for iBooks (within the iOS Settings app).

On your Mac, create a collection and add a PDF to it. It should then appear on your iDevice.