use strict;
use warnings;

my $path = "c:/path/to/files";

my $maxsize = 1048576;

opendir my $dirhandle, $path or die $!;

foreach my $file ( readdir $dirhandle ) {
    next unless -f $file;
    next unless -s $file > $maxsize;
    my $count = 0;
    open my $in, '<', "$path/$file" or die $!;
    {
      local $/ = \$maxsize;
      while ( my $record = <$in> ) {
        my $outname =   "$file.split" 
                      . sprintf "%03s", $count++;
        open my $out, '>', "$path/$outname" or die $!;
        print $out $record;
        close $out or die $!;
      }
    }
    close $in;
}