Question

How would it be possible to search for a string e.g. #Test1 in a text file and then output the line below it as a string e.g.

Test.txt

#Test1
86/100

#Test2
99/100

#Test3
13/100

so if #Test2 was the search keyword “99/200” would be turned into a string

Answer 1

Parse the file once, store the results in a dictionary. Then lookup in the dictionary.

var dictionary = new Dictionary<string, string>();
var lines = File.ReadLines("testScores.txt");
var e = lines.GetEnumerator();
while(e.MoveNext()) {
    if(e.Current.StartsWith("#Test")) {
        string test = e.Current;
        if(e.MoveNext()) {
            dictionary.Add(test, e.Current);
        }
        else {
            throw new Exception("File not in expected format.");
        }
    }
}  

Now you can just say

Console.WriteLine(dictionary["#Test1"]);

etc.

Also, long-term, I recommend moving to a database.