KatrinaMarzuki,
If you are refering to your Product Key which is required for Product Activation, it depends upon how you purchased your Office product.
If you purchased a retail product, then the Prodcut Key is on a yellow-orange sticker located within the CD holder of the product's retail box.
If you purchased office preinstalled on a computer, then most often the manufacturer includes the product CD's in a plain white cardboard or paper envelope, and typically the Product Key would be printed on a label on the envelope.
Hope this helps!