BitLocker is included in the following editions of Windows 7: Windows 7 Ultimate Windows 7 Enterprise

It is for Windows 7 Home, Starter, or Professional editions. If you have a supported edition, the feature is already installed; you simply need to activate it via the Control Panel. How to Enable BitLocker on Supported Versions If you are running Windows 7 Ultimate or Enterprise 32-bit:

While you cannot "download" BitLocker as a standalone app for Windows 7, it is a built-in feature of the operating system's most advanced versions. If you are looking for BitLocker on a 32-bit system, here is how to find it or get an equivalent solution. Availability on Windows 7 (32-bit)