I downloaded an email attachment.
I opened the Downloads app and saw the filename extension was not acceptable.
I renamed the file (xxx.txt) with ES3 File Explorer.
I shutdown the Nexus 7 - 2013.
I restarted the Nexus 7 - 2013.
I opened the Downloads app and the filename is unchanged.
When I try to select the file the app reports "Can't open file".
When I open ES3 File Explorer and select the file I'm optioned to use either ES Note Editor or HTMLViewer to read/show the file (successfully).

How do I get Downloads app to forget the old filename?

Thanks, Morris