Notepad beats them all?

Question

Notepad reads files by first mapping them into memory, rather than using the "usual" file reading mechanisms presumably used by the other editors you tried. This method allows reading of files even if they have an exclusive range-based locks.

You can achieve the same in C# with something along the lines of:

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))
{
    var l = r.ReadToEnd();
    Console.WriteLine(l);
}