To split on a string you need to use the overload that takes an array of strings:
string[] lines = theText.Split(
new[] { Environment.NewLine },
StringSplitOptions.None
);
Edit:
If you want to handle different types of line breaks in a text, you can use the ability to match more than one string. This will correctly split on either type of line break, and preserve empty lines and spacing in the text:
string[] lines = theText.Split(
new[] { "
", "
", "
" },
StringSplitOptions.None
);
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