You do not add the .dll instead you use the merge modules. When you click on the merge modules the property box in VS Studio populated. I forget where this is but look through the properties and you will find one labeled keycode. That is where you enter keycode. You get the key code from the menu option under help About Visual Studio. When you open that you will see a listbox showing the various Visual Studio items installed, one of those will be Crystal Reports. Cick on CR so it is highlighted then select copy info. I always paste the code to Notepad. You will see the long number broken down by hyphens. That is the keycode. It is not the registration number.
I am using CR2008 and this is now several versions ago, but I believe this is still is the correct instructions. If not I hope someone on the forum will correct any errors on my part.
Hope this helps