If you want to compare two files on disk that are not checked in to TFS, by using Microsoft Visual Studio, you can use the following steps:
1. Open Microsoft Visual Studio > Team Explorer > Source Control
2. Navigate to a random file en right click it:
3. Click on Compare…
4. For the Source Path: Click Browse… > Local Path… and browse to the first file.
5. Repeat this for the target path
6. Click OK
Now the two files will be compared and the differences will be shown, without the files being checked in to TFS.