The Gold Trade Pro Expert Advisor (EA) you're referring to seems to be a proprietary or commercial EA that is specifically designed to trade gold (XAU/USD). Unfortunately, as with most commercial EAs, the MQ4 source code is typically not publicly available unless the developer provides access to it. Developers generally distribute the EX4 compiled file, which is executable in MetaTrader 4 (MT4), but not the underlying MQ4 source code, to protect their intellectual property and prevent unauthorized modifications or replication.