In order to be used, the saved game files should be in their original location (most likely C:\Users\\Documents\The Witcher\saves in Windows systems, or ~/.local/share/cdprojektred/witcher2/GameDocuments/Witcher 2/gamesaves in SteamOS/Linux systems) and have been created during the Ice Plains or Order of the Flaming Rose Cloister portions of the Epilogue.
When starting a new game of The Witcher 2: Assassins of Kings, you can import a saved game from The Witcher by selecting 'New Game' then 'Import Witcher 1 Save' from the main menu.
1 From The Witcher to The Witcher 2: Assassins of Kings.
