Remove lines from Text file c#

first read the text in, line by line.
for each line check the first 10th chars. If they are not an “invalid char” (tab or space) include the line in the final string. Then store the final string. (you can overwrite the original file if needed)

List<char> invalidChars = new List<char> {" ", ";"};
string finalString = "";
using (StreamReader sr = new StreamReader("TestFile.txt"))
        {
            //grab line
            String line = sr.ReadToEnd();
            //grab first 10 chars of the line
            string firstChars = line.substring(0,10);
            //check if contains 
            bool hasInvalidChars = false;
            foreach(char c in invalidChars)
            {
                if(firstChars.toLowerInvariant().IndexOf(c) == 1)
                   hasInvalidChars = true;
            }
            if(!hasInvalidChars)
                finalString += line + Environment.NewLine;
        }

 //now store results
 using (System.IO.StreamWriter file = 
        new System.IO.StreamWriter(@"results.txt"))
 {
    file.write(finalString);
 }

then break the line into pieces: