Notepad++ 3 Views (windows) open? [duplicate]
Actually, you can have a bunch of files opened at the same time; each file is in a different tab. Just use File Open, and select your files. The Move to Other View allows you to see two files side by side.
Added
For viewing more than 2 files side-by-side, you will need to open a second instance of the program and tile the 2 windows so you can see up to 4 files at once.
To open a second instance you can hit Alt+F6: Open two instances of Notepad++