If you download the template on a Mac an extension ".txt" may be appended to the file name (standing for text file). To open it in Jupyter, you must delete this extension. To do this, try the following:

  1. Navigate to the file in the Mac Finder, secondary click on the file, and select "get info" from the drop-down menu that appears.
  2. In the "get info" window that appears, edit the file name under the "Name & Extension" tab. Specifically delete ".txt" from the end of the file name so that .ipynb is now at the end of the file name.
Editing the file name directly in the Mac Finder does NOT change the actual file extension (as stored in the directory) but rather suppresses displaying the extension in the Mac Finder.