Below is the code to change hexadecimal file to readable format :-

1) Read the Hexadecimal file.

2) Convert the Hexadecimal code to asciii value.

3) Convert the asciii value to readable char format.

int size=15;
 char[] mChangedFileCharArray = new char[size];
 int chatInt=0;
int positionOfFile=0;
File file = new File(Environment.getExternalStorageDirectory(), getString(R.string.app_name) + "/" +sharedPreferenceManager.getOperatorName(getActivity())+"/"+DATA_FILE_NAME);

try
{
   FileInputStream in = new FileInputStream(file);
                                int read;
  while((read = in.read()) != -1)
        { 
            String hexString=Integer.toHexString(read);
      //reading content in hexadecimal file 
            int temp2=Integer.parseInt(hexString.trim(), 16);
     //changing the hexadecimal to asciii value
            mChangedFileCharArray[chatInt] = (char) temp2;
    //converting ascii value to readable character value and storing in char array
                  chatInt++;
                  positionOfFile++;

        }
String readString = String.valueOf(mChangedFileCharArray);
} catch (Exception e) {
                                e.printStackTrace();
                            }