Package declarations - none

You need a package declaration of Book::Reader otherwise getData() will live in the main package. Also if you want to export methods in the current package you don't need to put an ampersand (&) before the name¹, and @ISA and @EXPORT need to be package level variables e.g

package Book::Reader;

require Exporter;
@ISA    = qw( Exporter );
@EXPORT = qw( getData );

use strict;

sub getData { ... }
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HTH

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broquaint

¹ as chromatic notes in his node Exporter will treat &sub the same as sub in the @EXPORT list