How can I identify if a .exe file is 32-bit or 64-bit from C#

How can I determine if an .EXE file (not my application, not another running application, not a .NET application) is 32-bit or 64-bit in C#? The best I found is this and I'm guessing there's a native .NET call.

If you don't use third-party libraries or winAPI, here's a method that reads the header and gets the information.

enum PlatformFile : uint
        {
            Unknown = 0,
            x86 = 1,
            x64 = 2
        }
        static PlatformFile GetPlatformFile(string filePath)
        {
            using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read))
            using (BinaryReader br = new BinaryReader(fs))
            {
                fs.Seek(0x3C, SeekOrigin.Begin);
                int peOffset = br.ReadInt32();
                fs.Seek(peOffset, SeekOrigin.Begin);
                uint peHead = br.ReadUInt32();

                if (peHead != 0x00004550)
                    return PlatformFile.Unknown;

                fs.Seek(peOffset + 4, SeekOrigin.Begin);
                ushort machine = br.ReadUInt16();

                if (machine == 0x014c) // IMAGE_FILE_MACHINE_I386
                    return PlatformFile.x86;
                else if (machine == 0x8664) // IMAGE_FILE_MACHINE_IA64 or IMAGE_FILE_MACHINE_AMD64
                    return PlatformFile.x64;
                else
                    return PlatformFile.Unknown;
            }
        }