TProtectedRange.SecurityDescriptorXLSX Property
Returns the security descriptor of the protected range, for XLSX files. This is a string used if you are giving permissions to some users in the range. Note that because of the different security descriptor formats, FlexCel won't convert between security descriptors from xls and xlsx. Take a look at APIMate to see the descriptor of a particular file.
Syntax
Namespace: FlexCel.Core
public String SecurityDescriptorXLSX { get; set; }