Typical Fruit-Co. arrogance, you either have an iDevice or else you are unwashed rubble and your needs are not important. Now why am I not surprised a bit about this? Yes, the reference by @nieldk points to the same specification mentioned in the stackoverflow answer. Ultimately the passbook file seems to be a zipfile containing a bunch of PNG images and some JSON data describing keys. If you are lucky one of the images might yield up an airline barcode in BCBP-2D format.