If your WinHelp system uses macros or custom DLLs, they will need to be changed for HTML Help. Instead of macros and DLLs, HTML Help can use most HTML-standard scripts in ActiveX or JavaScript. (The exceptions are scripts that call for a relative path. These might not work correctly in compiled HTML Help files, but might in uncompiled files.)

Most help authoring tools have the ability to convert at least some WinHelp macros into JavaScript. ForeHelp even enables you enter new macros using WinHelp syntax, and then converts them into JavaScript equivalents (but not all WinHelp macros are available). You need to find out which macros your help authoring tool can convert. Once you have made the conversion, you need to test to make sure that the features work the same way they do in the HTML Help file as they did in the WinHelp version.

You can expect to rewrite custom DLLs you created for WinHelp projects. Fortunately, there are ActiveX controls available that might do the same tasks. Research which ActiveX controls you want to use, but note any licensing costs and distribution restrictions if you want to use the controls in your help file.