Is there any built-in, add-in solution for visual studio to compare two files and display result with differences? I could\'t find one...
That functionality appears to be related to Source Control. So it is really as source control issue.
If you are not using Source Control - You should be - Try The Vault from www.sourcegear.com for a good (and free for one user) commercial source control system. There are others and they should come with a comparision tool (The Vault has one and its installed into VS when you install the vault client and connect to a source controlled project).