If you mean file comparing as in comparing a file on your computer and another file on the remote computer, you can do two things:
You can either send that file to your computer (with the File Transfer dialog) and compare them (with software or not (diff?)) as is, or you can send your file to the remote machine and compare them from there (although comparing on your local computer would be quicker)
You can open the file on your machine (if it is, say, editable text, like a configuration file) and open the file on the remote machine compare from screen to screen, although that would be fairly slow and typically painful.
..but although I looked, I can't find any built-in feature in Teamviewer that will enable you to compare files between your machine and the remote machine.