sub ShowPDF {
  my $pdf=shift;

  my $action = {
      MSWin32 => sub { $pdf=~s/\//\\/g; qx/explorer.exe "$url"/; },
      darwin  => sub { system qq{open "$pdf" >/dev/null 2>&1 &} },
  }->{$^O}    || sub { system qq{xdg-open "$pdf" >/dev/null 2>&1 &} };

  $action->();
}