OneDrive encrypts the files you save in OneDrive for work or school when your files are "at rest," stored on the cloud, and in transit to your device.
In OneDrive for home, when you store your important files in Personal Vault, OneDrive syncs them to a BitLocker-encrypted area of your local hard drive. If the files are not stored in the Personal Vault folder, then you can manually encrypt them in Windows File Explorer:
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Right-click the file you want to encrypt and select Properties.
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On the General tab, select Advanced.
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Select the Encrypt contents to secure data check box.
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Select OK > Apply > OK.
