A C# base64 file converter.

Base64FileConverter.cs

using System;
using System.IO;
using System.Linq;

public static class Base64FileConverter
{

    public static string ToBase64(byte[] bytes)
    {
        if (bytes == null || bytes.Length == 0)
        {
            return string.Empty;
        }

        return Convert.ToBase64String(bytes);
    }

    public static string ToBase64(this string filename)
    {
        var filepath = filename.Contains('\\') ? filename : (Path.Combine(Directory.GetCurrentDirectory(), filename));

        if (!File.Exists(filepath))
        {
            return null;
        }

        return Convert.ToBase64String(File.ReadAllBytes(filepath));
    }

    public static byte[] ToBytes(this string base54String)
    {
        if (string.IsNullOrWhiteSpace(base54String))
        {
            return null;
        }

        return Convert.FromBase64String(base54String);
    }

    public static bool ToFile(this string base54String, string filename)
    {
        if (string.IsNullOrWhiteSpace(base54String))
        {
            return false;
        }

        var bytes = Convert.FromBase64String(base54String);

        var filepath = filename.Contains('\\') ? filename : (Path.Combine(Directory.GetCurrentDirectory(), filename));

        File.WriteAllBytes(filepath, bytes);

        return true;
    }        
}