Unless you provide a full path to the file, your program will look for it in the current working directory. You can put the file anywhere you like if you write the open
call as
open my $fh, '<', '/full/path/to/simap data.text' or die $!;
Or if you want to omit the path and put it in the current working directory, and you don't know where that is, then add
use Cwd 'abs_path';
print abs_path('simap data.text'), "\n";
and you will see where the program will look if you provide just a filename to the open
.