In HTML Help Viewer, you can access the title "Platform SDK Documentation."
The full Win32 API set is documented in the Win32 Application Programming Interface for Windows NT Programmer's Reference, available from Microsoft Press® and also distributed as part of the online Platform Software Development Kit (sdk).
Other titles related to Windows programming and calling Win32 APIs are listed in Additional Resources (in Calling Win32 Routines), which describes the Visual Fortran Online Bookstore.