public class CustomFontResolver : IFontResolver
{
    public static readonly CustomFontResolver Instance = new CustomFontResolver();

    public byte[] GetFont(string faceName)
    {
        string filePath = Path.Combine(AppContext.BaseDirectory, "src", "Admin", "Common", "Assets", "Arial", "arial.ttf");
        if (faceName == "Arial")
        {
            return File.ReadAllBytes(filePath);
        }
        throw new System.NotImplementedException();
    }

    public FontResolverInfo ResolveTypeface(string familyName, bool isBold, bool isItalic)
    {
        if (familyName == "Arial")
        {
            return new FontResolverInfo("Arial");
        }
        return null;
    }
}

string testString = "Here be PDF";
        GlobalFontSettings.FontResolver = CustomFontResolver.Instance;
        var myFont = new XFont("Arial", 10, XFontStyleEx.Regular);
        var document = new MigraDoc.DocumentObjectModel.Document();
        var section = document.AddSection();
        section.AddParagraph(testString);
        var pdfRenderer = new MigraDoc.Rendering.PdfDocumentRenderer();
        pdfRenderer.Document = document;
        pdfRenderer.RenderDocument();

if (Capabilities.Build.IsCoreBuild)
    GlobalFontSettings.FontResolver = new FailsafeFontResolver();