With Tabulizer you can access files that are located on your local file system, or they reside in a remote location, provided that's publicly accessible.
Likewise, for database queries, you can retrieve data from the same database as the CMS (Joomla, Wordpress) or from a remote database.
In both cases, your web server should be configured properly in order to allow remote access. For instance, if there is a firewall that blocks remote file access, the OpenSSL is not enabled, the curl and the allow_url_fopen are disabled at the same time, you will not be able to access remote content.