SQLite databases are not protected by a password so Adminer refuses to open them. It can require a password of its own instead:
php -S localhost:8080 in the directory and open localhost:8080, or upload the directory to a web server.
adminer-plugins.php requiring the password. Save it next to Adminer and log in again.
Everybody who can open the address can try to guess the password so use a strong one. Keep in mind that the database file can be downloaded by everybody if it is placed in a public directory.