If you purchased the EA, the developer is the only one with the MQ4 file. Most developers will not give away source code to protect their intellectual property, but they may provide updates or fixes if you are a verified customer. 2. Hire an MQL Programmer to "Re-Code"
Instead of searching for a decompiler, consider these safer paths:
Decompiling EX4 files without permission from the original author is in most jurisdictions and violates the MT4 license agreement. It is considered reverse engineering and can lead to account bans or legal action. Legitimate uses would require explicit consent from the code owner.