How to add PDF's to iphone 5 using itunes 11.x

You should have iBooks app on your iPhone before you do below steps

Connect your iPhone to iTunes, Open iTunes, Choose Books on top left hand side corner of iTunes window as shown below

Drag the whatever PDF's you want to sync with your iPhone onto iTunes Books' window then click on
iPhone button on top right hand side corner of iTunes as shown below

Choose Sync Books option as shown below

Select whatever PDF's you want to sync with your iPhone, then click on 'Sync' and 'Apply' buttons as shown below

Disconnect your iPhones from iTunes , open iBooks app , choose PDF ,you should able to see uploaded PDF's now.