This leads to the million-dollar question:

Disclaimer: This article is for educational purposes only. Do not decompile software without explicit permission from the copyright holder. The author is not responsible for any financial loss, malware infection, or legal action resulting from the use of decompilers.

If you purchased an EA or indicator, and ask for the source code. Some sellers provide MQ4 upon request for a small fee (or free if you have proof of purchase).

Many scammers also sell "EX4 decompiler services" on Fiverr or Upwork – they take your EX4, run it through a free tool, and charge you $50 for the broken output. Before trying any conversion, ask yourself: Do I really need to convert this EX4?

The free methods are unreliable, dangerous, and often illegal. The resulting MQ4 code, if you get anything at all, will be messy, uncommented, and prone to errors.