While Windows 7 Professional include BitLocker for the internal hard drive (that feature is reserved for Windows 7 Enterprise and Ultimate), it does include BitLocker To Go .

If you need to encrypt the internal hard drive on Windows 7 Professional, you would typically need to use a third-party tool (like VeraCrypt) or upgrade to Windows 7 Ultimate/Enterprise.

You can create a VHD on a computer that does support BitLocker, encrypt it, and then move that VHD file to your Windows 7 Professional machine. Once attached via Disk Management, it functions as an encrypted "vault" for your files.