If you want to add a certain feature to your Help file that Windows Help does not support, and you have programming experience for Windows (or access to someone who does), you can develop custom extensions to support the functions you need. Extending Help involves using the Windows software libraries, called dynamic-link libraries (DLLs). These libraries are commonly used in Windows applications, and most programmers for Windows are familiar with their construction and use. You can use calls to functions in the DLLs as Help macros by registering the functions in the Help project file.
This section provides a general discussion of these tools and describes the authoring tasks related to using DLLs in a Help file. As a Help author, you should understand the capabilities of these tools. To develop your Help file to its fullest potential, you’ll want to be fully informed about the opportunities they present.