The quick and dirty answer is that in Employee.pm, $object is not defined. Which is because in main.pl you call new Person ... instead of new Employee.

But there are no methods in Employee.pm: all of that codes runs at use time, called from main.pl.

For purposes of demonstration, you probably want to wrap the print in Employee.pm as a printme method, and call it from main, such as $object->printme().

Update:

Don't forget to change $object to the $self idiom.