FontDropDownList and PrivateFontCollection

        // Fixed Width fonts are displayed in bold in the drop down list

        static internal void PopulateFonts(FontDropDownList control, PrivateFontCollection pfc)
        {
            control.Items.Clear();
            List<FontDropDownList.FontFamilyData> fonts = new List<FontDropDownList.FontFamilyData>();
            using (Graphics g = control.CreateGraphics())
            {
                using (InstalledFontCollection installed_font_collection = new InstalledFontCollection())
                {
                    GetFontFamilyData(g, installed_font_collection.Families, fonts);
                }
                GetFontFamilyData(g, pfc.Families, fonts);
            }

            // Sort and remove duplicates from list

            fonts.Sort((first, second) => first.Name.CompareTo(second.Name));
            Int32 index = 0;
            while (index < fonts.Count - 1)
            {
                if (fonts[index].Name == fonts[index + 1].Name)
                    fonts.RemoveAt(index);
                else
                    index++;
            }
            control.Items.AddRange(fonts.ToArray());
        }

        static void GetFontFamilyData(Graphics g, FontFamily[] font_families, List<FontDropDownList.FontFamilyData> fonts)
        {
            foreach (FontFamily font_family in font_families)
            {
                fonts.Add(new FontDropDownList.FontFamilyData(font_family.Name, IsFixedWidth(g, font_family)));
            }
        }

        static bool IsFixedWidth(Graphics g, FontFamily ff)
        {
            if (ff.IsStyleAvailable(FontStyle.Regular))
            {
                using (Font font = new Font(ff, 10, FontStyle.Regular))
                {
                    return g.MeasureString("iii", font).Width == g.MeasureString("WWW", font).Width;
                }
            }
            return false;
        }