How to: Debug .NET Framework source
Applies to: 
Visual Studio 
Visual Studio for Mac
Note
This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here
To debug .NET Framework source, you must:
Enable stepping into .NET Framework source.
Have access to debugging symbols for the code.
You can choose to download debugging symbols immediately, or set options for later downloading. If you don't download symbols immediately, they'll download the next time you start debugging your app. While debugging, you can also use the Modules or Call Stack windows to download and load symbols.
To enable stepping into .NET Framework source
Under Tools (or Debug) > Options > Debugging > General, select Enable .NET Framework source stepping.
If you had Just My Code enabled, a warning dialog box tells you that Just My Code is now disabled. Select OK.
If you did not have a local symbol cache set, a warning dialog box tells you that a default symbol cache has been set. Select OK.
Select OK to close the Options dialog.
To set or change symbol source locations and loading behavior
Select the Symbols category under Tools (or Debug) > Options > Debugging.
On the Symbols page, under Symbol file (.pdb) locations, select Microsoft Symbol Servers to access symbols from the public Microsoft Symbol Servers. Select the toolbar buttons to add other symbol locations and change the loading order.
To change your local symbols cache, edit or browse to a different location under Cache symbols in this directory.
To download symbols immediately, select Load all symbols. This button is available only while debugging.
If you don't download symbols now, they'll be downloaded the next time you start debugging.
Select OK to close the Options dialog.
To load symbols from the Modules or Call Stack windows
During debugging, open the window by selecting Debug > Windows > Modules (or press Ctrl + Alt + U) or Debug > Windows > Call Stack (Ctrl + Alt + C).
Right-click a module for which symbols weren't loaded. In the Modules window, symbol loading status is in the Symbols Status column. In the Call Stack window, status is in the Frame Status column, and the frame is grayed-out.
Select Load Symbols from the menu to locate and load symbol files from a folder on your machine.
Select Symbol Load Information to show the locations the debugger searched for symbols.
Select Symbol Settings to open the Symbols page. On the Symbols page, under Symbol file (.pdb) locations, select Microsoft Symbol Servers to access symbols from the public Microsoft Symbol Servers. Select the toolbar buttons to add other symbol locations and change the loading order. Select OK to close the dialog.