They are just serialized Windows properties. You can write and read these files (as streams) using builtin Windows implementation of IPropertyStore, for example using the PSCreateMemoryPropertyStore function

Here is a small sample console app that creates a test.props file with one property of string type:

#include <windows.h>
#include <atlbase.h>
#include <atlcom.h>
#include <propsys.h>
#include <propkey.h>
#include <propvarutil.h>

// some COM error handling useful macros
#define WIDEN2(x) L ## x
#define WIDEN(x) WIDEN2(x)
#define __WFILE__ WIDEN(__FILE__)
#define SBTRACE wprintf
#define CHECKHR(expr) {hr=(expr);if(FAILED(hr)){ SBTRACE(L"HR FAILED line:%u file:%s\n", __LINE__, __WFILE__); goto cleanup; } }  
#define HR HRESULT hr=S_OK;

int main()
{
  HR;
  PROPVARIANT pv;
  PropVariantInit(&pv);
  CoInitialize(NULL);
  {
    CComPtr<IPropertyStore> ps;
    CComPtr<IPersistStream> pstream;
    CComPtr<IStream> stream;

    // create the in-memory store
    CHECKHR(PSCreateMemoryPropertyStore(IID_PPV_ARGS(&ps)));

    // define some PROPVARIANT value (here it's a string)
    CHECKHR(InitPropVariantFromString(L"hello world", &pv));

    // any property key would work
    CHECKHR(ps->SetValue(PKEY_ItemNameDisplay, pv));

    // get IPersistStream to be able to load or write
    CHECKHR(ps->QueryInterface(&pstream));

    // create a file stream
    CHECKHR(SHCreateStreamOnFileEx(L"test.props", STGM_WRITE | STGM_CREATE, 0, TRUE, nullptr, &stream));

    // this sample only saves, but you can load from an existing stream
    CHECKHR(pstream->Save(stream, TRUE));
  }

cleanup:
  PropVariantClear(&pv);
  CoUninitialize();
  return 0;
}

Here is the result: