Modern EX4 files compiled with recent MT4 builds include:
There are paid decompilation services (costing $500-$3000). However:
MetaQuotes (the developer of MT4) has never released a tool to convert EX4 back to MQ4. They consider decompilation a violation of their license agreement and a threat to developers.
If you understand what the EX4 does (e.g., "it buys when RSI is below 30 and MACD crosses up"), you can write your own version. This is 100% legal and makes you a better programmer. Use the EX4 as a functional specification, not as source code to steal.