You’re looking at two copies of a text file. They’re different sizes, so you know something has changed. But what?
Text Compare is a tiny (<50KB download), free and portable tool which should be able to tell you more.
Launch the program and you must first point it at your target files (or just drag and drop them onto the appropriate file name boxes).
Clicking "Compare and show all" then displays the files in two separate text boxes, and highlights any lines (but not the individual characters) which are different.
The program doesn't use a simple linear comparison. It’s smart enough to recognize files which just have a different encoding. It can also recognize when lines have been inserted, copied or deleted, and lines which have moved up or down as a result are highlighted in a different color.
You can scroll through either text box to examine that file in detail. There's no way to scroll both files at the same time for easy side-by-side comparison, but you can search for specific text or use the file’s line numbers to do that manually.
Alternatively, if you're only interested in the differences, the program can display those -- or just the moved/ copied lines, or the new/ changed lines -- with a click.
Text Compare's interface is poor, there's no support for batch comparisons, and it can't save a report of file differences. But its multiple compare modes are a plus, and it’s also portable and no-strings free. If you just want to do occasional ad-hoc comparisons then the program might be worth a try.