C#

private string StringToNumberString (string inputString) {
    StringBuilder OutputBuilder = new StringBuilder("");

    byte[] ByteArrary = Encoding.ASCII.GetBytes(inputString);

    foreach (byte SingleByte in ByteArrary) {

        // Get the numeric value of this byte
        int ByteValue = Convert.ToInt32(SingleByte);

        // Convert this byte into 3 character string
        // "Right(3)" is an extension method that will return rightmost (x) characters
        string ByteValueString = ("000" + ByteValue.ToString()).Right(3);

        // Add this characters numeric string 
        OutputBuilder.Append(ByteValueString);
    }

    return OutputBuilder.ToString();
}

MadMyche wrote:

// Get the numeric value of this byte
int ByteValue = Convert.ToInt32(SingleByte);

// Convert this byte into 3 character string
// "Right(3)" is an extension method that will return rightmost (x) characters
string ByteValueString = ("000" + ByteValue.ToString()).Right(3);

// Add this characters numeric string 
OutputBuilder.Append(ByteValueString);

• No need to convert to an Int32 - a Byte is already numeric;
• No need for custom padding or extensions methods, when the built-in format strings will do the work for you;

string ByteValueString = SingleByte.ToString("D3");
OutputBuilder.Append(ByteValueString);

// requires your project has a reference to System.Numerics, and a using statement foe it

Guid g = Guid.NewGuid();
byte[] b = g.ToByteArray();
BigInteger bigI = new BigInteger(b);

string s0 = g.ToString();
string s1 = System.Text.Encoding.Unicode.GetString(b);
string s2 = System.Text.Encoding.UTF8.GetString(b);
string s3 = System.Text.Encoding.ASCII.GetString(b);
string s4 = bigI.ToString();

Console.WriteLine($"guid to string: {s0}\r\nbyte[] to Unicode string: {s1}\r\nbyte[] to UTF8 string: {s2}\r\nbyte[] to ASCII string: {s3}\r\nbyte[] to BigInt to string: {s4}");