next if $File::Find::name eq '.' or $File::Find::name eq '..';
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$File::Find::name contains the full path name so (in your example) it would start at ./. and continue with ./subdir/. etc. and would never match . or ...    Also you should use return when exiting from a subroutine.    Probably better as:

    return unless -f;
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    open my $file, '<', $File::Find::name or die "Error openning file:
+ $!\n";
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Also, because File::Find::find() changes directories, trying to open $File::Find::name from the current directory when using relative directory names won't work.    Just use the file name in $_:

    open my $file, '<', $_ or die "Error openning '$_' $!\n";
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