In the past when I have needed to manually register DLLs they have been C++ or VB ones which are registered using the regsrver command.
A recent project for a client was done using C# which requires the assembly to be registered using a different command. I am posting this here as a reminder to myself next time I need to do this.
When you register the assembly, you may receive a warning message about registering unsigned assemblies using the /codebase switch which is intended only with signed assemblies. If you trust the origin of the assembly then you can safely register the assembly and ignore the warning.
To register the .NET DLL, open a command prompt and type the following (the highlighted section is the name of the assembly being registered):
%SystemRoot%\Microsoft.NET\Framework\v4.0.30319\regasm.exe reportprinter.dll /codebase
To unregister a .NET DLL type the following:
%SystemRoot%\Microsoft.NET\Framework\v4.0.30319\regasm.exe reportprinter.dll /unregister
The highlighted section is the dll being registered or unregistered.