Hi,
Depending on your drop down setting, there will two different way to refer to the changed value.
If you're using just the "List Items" scripts will be;
if (xfa.event.newText == "proforma invoice"){
xfa.host.messageBox("make sure the name and email is entered");
}
If you're using "Specify Item values" with the "List Items", scripts will be;
if (this.boundItem(xfa.event.newText) == "1"){
xfa.host.messageBox("make sure the name and email is entered");
}
both scripts goes to change event of the drop down in javascript.