When you select a file – it does not show the extension

The utility then defaults the import to a .txt in error, even though the file has a different extension
It should use the extension of the file selected via the browse function.

To reproduce, try to import a file named "1".  The tool tries to import 1.txt.

We should check if a file with the user-specified name actually exists before applying the extension logic (or not apply the logic at all).