Others have pointed this out already, but I'll try to explain a little more. The safest way to pass hashes is to pass-by-reference, or pass a reference to the hash instead of passing the hash itself.

You could do this:

  use Converter;
  my $document = new Converter;
  my %convert_args_hash = (
    'MIME-Type' => 'application/ms-word',
    'Input' => '[In file]',
    'Output' => '[Out file]'
  );
  my $convert_args_hashref = \%convert_args_hash;
  my $status = $document->convert($convert_args_hashref);
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Or you could do as someone already suggested and use the anonymous hash constructor curly braces (which creates a reference to an anonymous hash), like this:

  my $status = $document->convert(
    {
      'MIME-Type' => 'application/ms-word',
      'Input' => '[In file]',
      'Output' => '[Out file]'
    }
  );
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and then in the "convert" method (subroutine) you would just accept the hashref as the one and only argument, something like this:

   sub convert {
      my $args_hashref = shift;
      print "The MIME-Type parameter = $args_hashref->{'MIME-Type'}\n"
+;
      ### blah blah ###
   } # end sub convert
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Hopefully you get the idea.

HTH.