libz.1.2.5.dylib(Xcode 4.5) 

libz.dylib 更名为libz.1.2.5.tbd

官方文档

A file ending in the extension  .dylib  is a dynamic library: it‘s a library that‘s loaded at runtime instead of at compile time. If you‘re familiar with DLLs from Windows or DSOs, it‘s more or less the same type of thing with a few twists. The Dynamic Library Programming Topics  section of the Mac OS X Developer Library covers all the details about the format and what you should be aware of.

libz.dylib  is the dynamic library for  Zlib , a general compression library. PDFs can (and usually do) use zlib to compress different aspects of the data contained within them, but accessing the PDF data at that level is pretty low-level, and higher-level libraries would abstract most of that type of stuff.

libz.1.2.5.dylib与libz.1.2.5.tbd