Check if a DLL is signed C++

I am trying to check if a DLL is signed based on the file path. I see that there are pre-existing solutions for this type of problem using WinVerifyTrust, however, when I tried checking it against "C:\Windows\System32\kernel32.dll" it said: "The file "C:\Windows\System32\kernel32.dll" is not signed." although kernel32 should be a signed dll. I am on Windows 7 fyi.

This is the source code to the function I called: https://msdn.microsoft.com/en-us/library/windows/desktop/aa382384(v=vs.85).aspx

How can I fix the function?