The password seems to be "malte". The executable is completely unobfuscated .NET, and all you need for "reverse engineering" is ILSpy or DotPeek.

    public static void ExtractFile(string apbx, string file, string targetDir, bool recursive = false)
    {
      if (recursive)
        APBX.RunCommand("x \"" + file + "\" -o\"" + targetDir + "\" -p\"malte\" -y -r");
      else
        APBX.RunCommand("x \"" + apbx + "\" -o\"" + targetDir + "\" -p\"malte\" \"" + file + "\" -y -r-");
    }

    public static void ExtractArchive(string apbx, string targetDir, string exclude = null)
    {
      if (exclude != null)
        APBX.RunCommand("x \"" + apbx + "\" -o\"" + targetDir + "\" -p\"malte\" -x!\"" + exclude + "\" -y");
      else
        APBX.RunCommand("x \"" + apbx + "\" -o\"" + targetDir + "\" -p\"malte\" -y");
    }