Based on PDF Reference Version 1.3, this Version 1.4 adds new content and has corrected lots of printing errors and bugs in the previous version. The most significant part is the introduction of the transparency imaging model, which is covered by an entire chapter as well as parts of other chapters. However, the whole book does not have any example regarding the transparency model. In Appendix G, the example G.3 (same as the one in Version 1.3) shows a default opaque model. It would have been nice if there were a corresponding example of the transparency model. A good simple example wins over thousands of words.