A quick Google search for "how to convert ex4 to mq4 free work" returns thousands of links promising magical solutions, shady software, and "100% working decompilers."
No, you cannot get the original MQ4 with variable names, comments, and structure exactly as the author wrote it. Long answer: Yes, you can generate a working, recompilable MQ4 file from an EX4 using decompilation tools. The result will be: