Just bought a ticket to advanced screening of Paper Towns, and this voucher was attached at the bottom of the ticket.
It's supposed to be exclusive to movie-goers, but the code looks generic.
Terms and conditions: BW-YAFAN15 is a 15% off voucher code and is only redeemable on young adult books and excludes all other books, CDs, DVDs, Blu-rays, eBooks, eReaders, stationery, calendars, gifts, and accessories. Offer valid until midnight (AEDST) Friday 31 July 2015. Voucher code cannot be used in conjunction with any other offer. Bookworld reserves the right to cancel or alter the promotion should it be deemed necessary.
NOTE: Bookworld often isn't the cheapest place for books. I highly suggest you check Booko before purchasing anything. If it is one of the cheapest, now you can make it even cheaper!!