for $file (@files){
     $string = "open (A$file, \"perl part2.pl $file|\")";
     eval $string; # Error checking omitted for simplicity
 }
[download]

No good read to use eval for that.

  use Symbol qw( gensym );
  for $file (@files){
      open( my $fh= gensym(), "perl part2.pl $file |" );
      # Error checking omitted for simplicity
  }
[download]

And since you don't seem to be doing anything with the pipe that you open, I'd suggest:

  for $file (@files){
      system( 1, "perl part2.pl $file" );
      # Error checking omitted for simplicity
  }
[download]

But there are quite a few ways to start a process in the background under Win32. I'm not a big fan of Win32::Process which I think was poorly written, is usually overkill, and is very unportable to other operating systems. You can find many of them mentioned in the 3 or 4 other threads on this topic that have shown up in the last few weeks or even in Q&A. But I like the very portable (and probably still not officially documented) system(1,...).