The command line that builds the help files is set up when the XLL+ project is created. It includes the names of any source files that contain add-in functions, as well as any extensions used by the add-in functions, e.g.:
"$(Xlp90InstallDir7)bin\BuildHelp.exe" -s "$(ProjectDir)." -i "$(ProjectName).cpp" -p $(ProjectName) -n true" "$(Xlp90InstallDir7)bin\BuildHelp.exe" -s "$(ProjectDir)." -i "$(ProjectName).cpp" -i "AnotherFile.cpp" -p $(ProjectName) -n true -e "RtdHandles.xpe"
For more details about the command line tool that builds help files, see the BuildHelp Utility reference.
From time to time you may need to update the command line:
You should use the Update Help Command Line command to update the command line. After you run it, the help command line will be updated to include all relevant source files and extensions.