Purchasing a "product key" online for Office 2013 is risky and requires caution.

When you purchase Microsoft Office 2013, you'll receive a product key that corresponds to the specific version and edition of the software you've bought. When you install the software, you'll be prompted to enter the product key. Once entered, the software will verify the key with Microsoft's servers to ensure it's valid and hasn't been used before.

Microsoft Office 2013 is generally considered a significant and well-regarded update to the suite, introducing a more tablet-friendly interface and improved document management over Office 2010. However, if you are looking for a product key today, there are several critical factors to consider regarding legitimacy, support, and activation.