I have read this question to get first char of the string. Is there a way to get the first n number of characters from a string in C#?
Append five whitespace characters then cut off the first five and trim the result. The number of spaces you append should match the number you are cutting. Be sure to include the parenthesis before .Substring(0,X) or you'll append nothing.
string str = (yourStringVariable + " ").Substring(0,5).Trim();
With this technique you won't have to worry about the ArgumentOutOfRangeException mentioned in other answers.