sub GetNthDocument {
    my ( $Collection, $n ) = @_;

    return undef if $n < 1;

    my $doc = $Collection->GetFirstDocument;
    my $ix = 1;
    while ( $ix < $n and $doc ) {
        $doc = $Collection->GetNextDocument( $doc );
        ++ $ix;
    }

    return $doc;
}