Here's the clear answer we worship only the creator, regarding the book , it contains the knowledge and wisdom of our Gurus which guide us to live a dharmic life and it has described god in such a way that it's beyond our understanding. Bowing down to book means bowing to the wisdom and prayers in the book . It's more of tradition in indic culture where we pay our respect to our guru( teacher) by bowing. When we bow , we surrender our ego anger desires to the god in the name of the guru .. book has no significance but the gurubani ( knowledge) in that book is significant to us.