question

If I have a php database connection established in a file on a project name database.php and I am using require_once(' database.php'); on whatever other files I want to establish that connection with, Can I set up multiple database connections in that database.php file and assign each one to its own PDO and use them through the same require_once connection, allowing me to use whatever database I need throughout a file by there distinct PDO name, allowing me to pull data from many other databases perhaps combing them on a php file?