You constructor (openForRead) returns the last expression evaluated, $fh. But this is an object of a different class - IO::File. You blessed \$filename to your class, not the handle, and you did not return it.

Moreover, $fh is declared with my in the package. Why? Do you want to keep the same file handle for all the instances of the class? Just create a fresh new reference in the constructor and use idiomatic my $self = shift; in other methods.