One of the important skill in trading is one should be able to educate an EA. A good decompiler like EX4-TO-MQ4 is needed to educate EA. But then, what dissassembler should we use if the EA has a DLL? After that, what modifying code should be use after? How to unpack DLLS. Steps vary from easy to pretty complicated ones. The only option for C/C++ AFAIK is IDA Pro. You need, however, a pretty good deal of understanding for you to do it properly. If something is translated from ASM to C, its structure and the functions is lost since ASM is pretty hard and complicated language system. When you try decoding it, it will never go back to its original look or it will not look the same again. If the system is written in .NET, the .NET reflector would work well.
You may also use EX4- To-MQ4 when decompiling ex 4-file and IDA when decompiling DLL. For file management like comparing, copying, extracting, viewing and compacting etc, you may use Total Commander with Notepad++ as the editor. ex4-to-mq4_v188.8.131.52 doesn’t work on all expert.
Another expert advice one should be able to learn first programming in general before taking any step to learn MQL4. This is so that there are very little good educational material for learning MQL4 while a lot of educational material can be found to learn programming and also MQL4 is not an easy language to learn. Even if you will learn the steps in MQL4 solution, you will end up wandering since you have no knowledge in computer programming. You may start off with ISO Pascal, and then move to learn C and Java. You may start learning MQL4 while you are learning computer programming from scratch.