A Diff Utility makes this an easy task. It is a utility program that compares two files and highlights the differences. There are many available, either free or paid for. Some just work with source code, while others will do comparison of binary code. Some version control systems and IDEs have a diff utility built in.
All diff utilities show differences between two files. The more powerful can compare files in one directory against another and even allow you to merge the differences between files.

