.NET Reactor
User guide

Merge Assemblies

Enable this option to merge multiple assemblies into a single target assembly. .NET Reactor takes your assemblies (Main Assembly and assemblies listed in Additional Files) and merges them into one target assembly.
Merging dependencies improves the protection of your software. The merged dependencies are no longer visible to the user and as they are a real part of the main assembly they are automatically protected as well. In case the main assembly is an executable, the target assembly is still an executable with the same entry point.
3rd party libraries are often already protected and it is not recommend to merge them with the main assembly. If you have troubles merging assemblies you should embed them inside the main assembly instead.
*Disable this option to protect assemblies listed in Additional Files separately.