Kindle to Calibre troubleshooting

Hello there!

I am trying to add a kindle book to Calibre (for the purposes of converting it to a PDF). I downloaded Calibre (6.9) to my Mac (Ventura 13.0.1), installed it into my Applications folder. When I try to add a new book in Calibre, I get the following message (any help would be greatly appreciated - than you in advance!!) :

WARNING: Errors while adding: There were problems adding some files, click "Show details" for more information


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Failed to add the file /Applications/Kindle.app to the book: /Applications/Kindle
With error:
Traceback (most recent call last):
File "calibre/gui2/add.py", line 487, in add_formats
File "calibre/db/cache.py", line 1810, in add_format
IsADirectoryError: [Errno 21] Is a directory: '/Applications/Kindle.app'