Look through your MQL4/Indicators or MQL4/Experts folders on older PC installations or VPS backups.

: In early 2014, MetaQuotes updated MT4 to Build 600+, which completely changed how files are compiled. Modern .ex4 files use advanced encryption and a different binary structure that this 2014 decompiler cannot process. Key Functionality and Steps

The "v40427" (version 4.0.427) decompiler was originally released by purebeam.biz around 2009–2014. Compatibility: It only works on very old MT4 files (Build 509 or lower). Modern MT4: