You can attach NProfiler to .NET processes that are already running. However, this comes with some limitations, so it is usually better to use one of the other profiling session types:
Start NProfiler. The session configurator opens automatically. Alternatively, click Home → Session → New in the ribbon to open the session configurator.
Select the application type “Attach to Running .NET 4+ Process” at the top.
Required. Select one or more processes to which NProfiler should be attached. These must be processes that have loaded .NET runtimes. You can use the search box above the process list to search by name, title, or process ID. You can also sort the list by clicking on the column headers.