Let me give you the short, honest answer first, then the long, technical one.
Ask below, but please do not ask for links to decompilers. They are against the rules.
A: No. Decompiling is generally prohibited by the EULA, even for personal use. MetaQuotes explicitly forbids reverse engineering in their license agreement.
How to Convert EX4 to MQL4: A Complete Guide to Decompiling MetaTrader 4 Files
Before attempting to convert an EX4 file, you must consider the legal implications:
To understand why conversion is difficult, one must understand compilation.
Decompiling a paid EA from the MQL5 Market usually violates terms of service and copyright law. 4. How to Prevent Needing a Conversion