A .cbr file is a compressed file that allows a set of comic book images to be stored. These images can be ordered and the format in which they are displayed can be altered to allow two images to be viewed side by side, in the same way as a double page spread would occur.
A .cbz file is actually just a .zip file with an amended file extension. What makes a .cbz file different is that it can be opened directly by comic book viewer applications without a requirement to decompress it first. The user can also associate the file extension with a comic book viewer application. Typical image formats are allowed for a .cbr file such as JPEG, GIFF, TIFF and PNG.
PDF is a file format developed by Adobe Systems for representing documents in a manner that is separate from the original operating system, application or hardware from where it was originally created. A PDF file can be any length, contain any number of fonts and images and is designed to enable the creation and transfer of printer-ready output.
Each PDF file encapsulates a complete description of a 2D document (and, with the advent of Acrobat 3D, embedded 3D documents) that includes the text, fonts, images and 2D vector graphics that compose the document. They do not encode information that is specific to the application software, hardware, or operating system used to create or view the document.