What that describes is what can work if you know the complete filepath to the specific file. You can't use it with a wild card and you can't use it with a dialog that opens for the user to select a specific file.
You may want to investigate one of the plug ins that offer options for listing folder contents and manipulating files and folders instead of just using FileMaker's built in capability.
You can also just have Insert File open a dialog for the user to select a file by not specifying any file, but you then do not have any direct control over what folder contents will first appear in the dialog.
Thanks for the very quick response, PhilModJunk. I will look for a plugin and/or try your second suggestion.