PrivateFontCollection is failed to add memory font under .Net Core

Question

I need to add a set of fonts to PrivateFontCollection. For some reason this task should be accomplished by using AddMemoryFont function.

    var fontCollectionFromMemory = new PrivateFontCollection();
    var fontCollectionFromFile = new PrivateFontCollection();
    foreach (var file in Directory.GetFiles(@"C:\Windows\Fonts", "*.ttf"))
    {
        using (var stream = File.OpenRead(file))
        {
            var fontData = new byte[stream.Length];
            stream.Read(fontData, 0, fontData.Length);
            var fontDataPtr = Marshal.AllocCoTaskMem(fontData.Length);
            try
            {
                Marshal.Copy(fontData, 0, fontDataPtr, fontData.Length);
                fontCollectionFromMemory.AddMemoryFont(fontDataPtr, fontData.Length);
                Thread.Sleep(100);
            }
            finally
            {
                Marshal.FreeCoTaskMem(fontDataPtr);
            }
        }

        // fontCollectionFromFile.AddFontFile(file);
    }
    Console.WriteLine($"PrivateFontCollection's size(filled via AddMemoryFont): {fontCollectionFromMemory.Families.Length}");
    Console.WriteLine($"PrivateFontCollection's size(filled via AddFontFile): {fontCollectionFromFile.Families.Length}");

After running the code above I get the following output:

PrivateFontCollection's size(filled via AddMemoryFont): 34
PrivateFontCollection's size(filled via AddFontFile): 0

This outcome is very confusing...

If I uncomment the following line:

fontCollectionFromFile.AddFontFile(file);

then I get:

PrivateFontCollection's size(filled via AddMemoryFont): 166
PrivateFontCollection's size(filled via AddFontFile): 198

This result is also confusing.

How these outcomes can be explained? What is a proper way to use PrivateFontCollection.AddMemoryFont?

Environment:

• Windows 10 Home

• .Net Core 2.2.106

• System.Drawing.Common 4.7.0