Importing a .Net assembly does not produce any diagram

Hi I was just checking a reverse engineering feature you have in the professional edition, the ability to import .NET assemblies. I am trying to import a .dll file that comes from a package that was downloaded off of nuget.

After importing, no diagram was produced, but a folder was inserted into my project tree.

Could you help me understand what I need to do correctly and explain what possible source assemblies can be imported.

Thanks!