Append a txt file to another txt file

Copy this method to your Global Class in AX.
public static void appendTextFile(str fromFilePath,str toFilePath)
{
    FileIOPermission fromPerm;
    FileIOPermission toPerm;
    System.String text;
    System.IO.FileStream fs;
    System.IO.StreamReader reader;
    ;
    if(System.IO.File::Exists(fromFilePath) &&
System.IO.File::Exists(toFilePath))
    {
         // Read text from file
        reader = new System.IO.StreamReader(fromFilePath);
        text = reader.ReadToEnd();
        reader.Close();
        // Append
        System.IO.File::AppendAllText(toFilePath,text);
    }
    else
    {
        throw error("Invalid path or file does not exist");
    }

}