The CHM file format was developed by Microsoft and first released along with Windows 98 and the format continues to be supported. This file format superseded WinHelp. CHM files grew in popularity due to the fact that they are fully compatible with a web browser which can be found on all computers. The vulnerability of this file type has been highlighted widely due to the ability for certain controls to be executed by the file.
A .chm file comprises of a number of HTML pages and an Index. The format supports 28 different language types. The file provides functionality such as compression, merge and search. Just like a HTML page, the file can be composed of a variety of tags and images to enrich the content of the help files.
Beyond CHM Internet Explorer Microsoft Reader Mozilla Firefox
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.