You can achieve your goal even without "opening" the folder: 
for my $file (glob 'C:/Users/ZB/Desktop/Text\ Files/*.txt') {
    calculate($file)
}

[download]
Update: Note the slashes separate the path elements and the backslash quotes the space.
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: Open a folder by choroba
in thread Open a folder by Dr Manhattan

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