This is the macro command that sets up and runs a Merge.
MergeRun (FormFileType: FormFile!; FormFile: "F:\examples\merge\date.frm"; DataFileType: DataFile!; DataFile: "F:\examples\merge\date.dat"; OutputFileType: ToCurrentDoc!)
Other macro commands can identify the folder and name of the current file or enable you to specify a folder and filename/s.
Then the macro could modify the command above to change the choice of merge folders and files.