User friendly name of the owner of the file.

using System.IO;
using System.Security.Principal;
using System.Security.AccessControl;

FileSecurity fs = File.GetAccessControl(@"C:\CERT\Thinking_in_C_\Thinking in C#.pdf");
NTAccount ntac = fs.GetOwner(typeof(NTAccount)) as NTAccount;
Console.WriteLine(ntac.Value);