How to read file as string in BinaryReader?

Question

C++ / C#

Stupid question, but I hope it helps.
In general, I'm trying to find a line in a binary file, add a byte and read the data after it and output it to the label. Problem with filling variable content, I tried like this

string content = File.ReadAllText(@"D:\Player.chr");

but when executed, it throws an exception that the file is busy, which is logical. Well, in general, probably the wrong approach. Tell me how to be right?

using (var file = File.Open(@"D:\Player.chr", FileMode.Open, FileAccess.ReadWrite))
            {
                using (var br = new BinaryReader(file, Encoding.Unicode))
                {
                    string content = ""; // тут надо считать в строку
                    var offset = content.IndexOf("money");
                    offset += "money".Length + 1;
                    br.BaseStream.Position = offset;
                    label1.Text = offset.ToString();
                }
            }