Library Mode is a per-assembly option that tells Dotfuscator not to rename or remove anything that could be accessed from outside that assembly.
Library Mode is enabled by default for all input assemblies. As a result, applications are likely to work after renaming. However, users may be concerned that so little of their application has been renamed. Turning Library Mode off will allow Dotfuscator to rename much more.
An exact specification of Library Mode rules can be found in the Dotfuscator User Guide.