You're wrong if you think obfuscation means complete renaming of all the names of namespaces, types, fields, methods and events without considering reservation of some names. Actually, some names can't be renamed. Otherwise, the obfucated version of the assemblies can't work. This applies both for Exe and Dll files.
The following topic applies for Standard Edition and Professional Edition Only.
For Dll files, What's best for Aspose.Obfuscator is, it can automatically reserve names for those interfaces which may be called by external applications, which guarantees your Dlls can work normally as an un-obfacated one.
This feature is very useful if you're a control, component or library developer. Of course, if you're an ASP.Net application developer, you can also benefit from this feature. You don't need to care about which names should be reserved as long as it can work when it is un-obfuscated.