This feature is only available for applications running on .NET Framework 4 or newer.
Also, it is not available in Silverlight.
Profiler can attach to a running application started without profiler.
The locally running .NET applications are shown on the Welcome screen:
Attach mode limitations
Not all profiling capabilities are available in the attach mode due to .NET Framework limitations listed below.
To get all capabilities, application should be started with the profiler.
Memory profiling is disabled for applications running in concurrent GC mode.
Read this MSDN article
to learn how to avoid using concurrent GC mode.
CPU tracing is not available. Use sampling instead.
Some threads started before attach will not be shown.
In particular, they will not be seen in the Threads view and in CPU sampling results.
To make some of the threads appear,
you may try to explicitly force garbage collection via corresponding toolbar button.