Memory map and read a file. From here: https://stackoverflow.com/questions/45644934/notepad-beats-them-all

FileUtils.cs

using System.IO;
using System.IO.MemoryMappedFiles;

public static class FileUtils
{
    public static string MapAndRead(string processIdPath) {
        using (var f = new FileStream(processIdPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
        using (var m = MemoryMappedFile.CreateFromFile(f, null, 0, MemoryMappedFileAccess.Read, null, HandleInheritability.None, true))
        using (var s = m.CreateViewStream(0, 0, MemoryMappedFileAccess.Read))
        using (var r = new StreamReader(s)) {
            return r.ReadToEnd();
        }
    }
}