it does not have library folder.
mate, don't use the program files to look Library. check in the program data and you'll see the library.
I dont have library folder, when i install proteus 8. Where do i add arduino library. At internet solution for proteus 7 is given but when i installed proteus 8 it does not have library folder.your program data folder is hidden...open local disk C...At the view menu in top of the screen choose hidden files...Now u can see your program data folder.....C/program data/labelectronics/proteus 8/library.....you can also find your library file location in system settings of proteus software