C++ - DirectWrite: Load font from file at runtime

I'm trying to load a font from a file at runtime and display it with DirectWrite. The following code should initialize a IDWriteTextFormat object with that font:

hr = pDWriteFactory->CreateTextFormat(
            L"Font Family",    // Font family name
            NULL,              // Font collection (NULL sets it to use the system font collection)
                               // Somehow, a custom font collection should be used here, but I don't know how to do that
            DWRITE_FONT_WEIGHT_REGULAR,
            DWRITE_FONT_STYLE_NORMAL,
            DWRITE_FONT_STRETCH_NORMAL,
            16.0f,
            L"en-us",
            &pTextFormat       // IDWriteTextFormat object
        );

It works perfectly with system fonts but I don't know how to load a custom font file. I would appreciate any examples on how to achieve that.

What I tried so far:
• I read this article and this question on Stackoverflow but I don't see where one should pass the file path of the font file (therefore, I completely failed to implement any of the code provided on those two pages)
• I also read this article but if I'm right, it has nothing to do with DirectWrite (?) (I tried to implement the AddFontResourceEx-method, but to no avail)
• Finally, the answer to this question suggested using ResourceFontContext::CreateFontCollection could solve the problem but after reading this page (it's in German but the screenshot is in English) I believe that it can only be used with fonts embedded as resources (which is not an option in my case)

Solution

Sure, it's possible to do that. You'll need to:

implement IDWriteFontCollectionLoader interface in your code;

You should also implement IDWriteFontFileEnumerator obviously, but this should be trivial.
register loader with the factory using RegisterFontCollectionLoader
create a collection using CreateCustomFontCollection and same factory;
pass it to CreateTextFormat called on same factory.

When you call CreateCustomFontCollection you have to provide a collection key and its size, it's a blob only meaningful to you, could be anything. Later on your loader will be called with this key, so you can identify it. For example you can use a string 'myspecialkey' as a key, and in CreateEnumeratorFromKey check if it's called with that key, rejecting any other key.

If you only wanted to create a fontface object from a path to a file, you don't need any of above, just use CreateFontFileReference followed by CreateFontFace.