And if you are building UI and wish to have more customization options you can use Pick File()
Names Default To Here(1);
filepath = Pick File(
"Select JMP File",
"$DOCUMENTS",
{"All Files|*"},
1,
0,
"newJmpFile.jmp"
);
If(IsMissing(filepath),
Throw("No file selected");
);
dt = Open(filepath);
-Jarmo