If you need to encrypt data on your HDD, you can turn on BitLocker.
“BitLocker helps keep everything from documents to passwords safer by encrypting the entire drive that Windows and your data reside on. Once BitLocker is turned on, any file you save on that drive is encrypted automatically.”
Therefore, you can create a passoword that will encrypt all files and folder on your drive.
1. Right click on the drive you need to encrypt