You're looking for information on the product key versus retail code for Company of Heroes: Opposing Fronts.
Installation Order: If using old discs, it is recommended to install Opposing Fronts first, then use the in-game "Add Product" option to register the original game key. You're looking for information on the product key
The first was his Retail Code. It was printed on the back of a glossy manual that still smelled of fresh ink, tucked inside a physical box he’d biked three miles to buy. It was his proof of "New" ownership—a physical artifact of the era. He typed it in, watching the progress bar crawl forward as the disc spun frantically in the drive, a mechanical roar that felt like a Tiger tank idling in his room. Reuse & transferability
If you have purchased a copy of the game and are having trouble finding or using your product key or retail code, try contacting the game's support team. How to install Company of Heroes: Modern Mods