The easiest way to convert them is to use a web service like freepdfconvert. If that's not doable and the box you're doing the converting on is windows (and you have MSWord installed and the version of MSWord can save as PDF) then Win32::OLE is probably the best approach:

  ...
  eval {
    my $consts = Win32::OLE::Const->Load( "Microsoft Word" );
    my $msword = Win32::OLE->GetActiveObject('Word.Application') ||
                 Win32::OLE->new('Word.Application', 'Quit') ||
        die "cannot get or create word: $!";

    $msword->{Visible}       = 0;
    $msword->{DisplayAlerts} = $consts->{wdAlertsNone};
    $msword->Documents->OpenNoRepairDialog( $in_filename ) ||
      die "cannot open $in_filename - ", Win32::OLE->LastError();

    $msword->ActiveDocument->SaveAs( {
      FileName   => $out_filename,
      FileFormat => $consts->{wdFormatPDF},
    } );

    $msword->ActiveDocument->Close( 0 );
  };
  ...
[download]

Update: I should have said if you're on *nix, there are other things you can do like going through OpenOffice or AntiWord but due to the nature of MSWord (or MS), using anything other than an MS approach will lead to a loss of *pixel perfection* for most documents. They may still be readable and usable but the converted document may look very different from the original.