I’m finally using this method :
First => ArrayOfString = String1.Split(Environment.NewLine.ToCharArray()) where String1 is my full text
Second => Initialization of an Index to 0 and
While Index < 25
String3 = String.Concat(String2, ArrayOfString(Index)
String2 = String3
Index = Index + 1
where String2 will be my final result and String3, an intermediate result.
At the end, i’ve my Result, String2, which contains my 25 first line of the initial text from which i wanted the split.
Thx all for your help 