File Protection encrypts a file so that it can only be opened with an encryption key. Encryption scrambles all of the data in the DGN file making it impossible to use the data until it is unscrambled. There are several ways to provide this key to users while keeping it secret.
By default, File Protection encrypts the file’s thumbnail image and summary properties. These items are shown by Windows File Explorer, by the File Open dialog, and by the File Properties dialog. To make either of these items unencrypted, set the MS_PROTECTION_NOENCRYPT_THUMBNAIL and/or MS_PROTECTION_NOENCRYPT_PROPERTIES configuration variables.