The product key is a long alphanumeric code used by software developers to keep a check on piracy and illegal installation of their applications. This code is used while installing any software which is licensed, and it is only with the help of this key that you can activate your product online and use it to the fullest. If you do not have this key, you might not be able to install the software, and even if the installer allows you to install it, still you will not be able to activate it online and the software will start restricting you to use all of its features if not activated. When a product is registered or activated, the machine address is saved at the servers so that it can be checked when you try to install it on another machine. If you purchase a single user copy of any software, you cannot activate it on multiple systems. If you use a friends’ product key for installing any software on your machine then again you would not be able to activate it on the Internet. So by these examples we can define how important a product key is and we should not share it with someone else. There may be situations where in you purchase software but somehow lose the product key. Though you are the owner of that software still you would not be able to install or re-install it again on your machine.
Below I have mentioned several ways by which you can recover your lost product keys.
CD Jacket: All software which shipped in CDs or DVDs, have their product keys mentioned on a sticker on the CD/DVD case/jacket. If you can find the CD/DVD case, you can know the product key.
E-mail: If you purchase a product online, the product key is mailed to you by the vendor. This can be the best way to find out the missing product key. All you need is access to the same e-mail account which you used while purchasing the software.
Customer Support: If you actually are the owner of the software, you can call the customer support of it or write to them stating your problem and they will certainly assist you out in getting the product key back. They will verify your identity with the information against your account in their records and will give you the product key back.
Third Party Applications: There are a number of tools available on the Internet which can let you know the product key of any software. The only prerequisite is that you should have the software installed on any computer using the product key which is now missing. Whenever you install any application using a product key, it gets saved in the Windows Registry either in simple text format or encrypted. These tools scan the Registry and fetch the saved product key for you.