Convert PDF to bytes[] and bytes[] to string and vice versa

//convert pdf to bytes
FileStream fs;
fs = File.Open(fileName, FileMode.Open);
byte[] bytBytes1 = new byte[fs.Length];
fs.Read(bytBytes1, 0, bytBytes1.Length);
fs.Close();

//convert bytes to string
string strModified = Encoding.Unicode.GetString(bytBytes1);

//convert string to bytes
byte[] b =Encoding.Unicode.GetBytes(strModified);

//to open the attachment
Response.AddHeader("Content-disposition", "attachment;filename=filename.pdf");
Response.ContentType = "application/pdf";
Response.BinaryWrite(b);
Response.End();