var textBodyListStyle = textBody.ListStyle;

using (var presentationDocument =
       DocumentFormat.OpenXml.Packaging.PresentationDocument.Open("测试.pptx", false))
{
    var presentationPart = presentationDocument.PresentationPart;
    var presentation = presentationPart.Presentation;

    var defaultTextStyle = presentation.DefaultTextStyle;
}

var defaultTextStyle = presentation.DefaultTextStyle;
var textBody = shape.TextBody;

var textBodyListStyle = textBody.ListStyle;

Debug.Assert(textBodyListStyle.ChildElements.Count == 0);

var paragraph = textBody.Descendants<Paragraph>().First();
var level = paragraph.ParagraphProperties?.Level?.Value ?? 1;
Debug.Assert(level == 1);
Debug.Assert(paragraph.ParagraphProperties == null);

var paragraphProperties = defaultTextStyle.Level1ParagraphProperties;

foreach (var run in paragraph.Descendants<Run>())
{
    var runProperties = run.RunProperties;
    var eastAsianFont = runProperties.GetFirstChild<EastAsianFont>();
    Debug.Assert(eastAsianFont == null);
    // 忽略代码
}

var paragraphProperties = defaultTextStyle.Level1ParagraphProperties;

eastAsianFont = paragraphProperties.GetFirstChild<DefaultRunProperties>()
    .GetFirstChild<EastAsianFont>();

var typeface = eastAsianFont.Typeface.Value;

Console.WriteLine($"字体是 {typeface}"); 

// typeface == "林德熙"

private static readonly Regex ThemeFontTypePattern =
            new Regex(@"(^\+(mn|mj)\-(lt|cs|ea)$)", RegexOptions.Compiled);

    public enum FontLang
    {
        /// <summary>
        /// lt
        /// </summary>
        LatinFont,

        /// <summary>
        /// ea
        /// </summary>
        EastAsianFont,

        /// <summary>
        /// cs 
        /// </summary>
        ComplexScriptFont,

        /// <summary>
        /// sym
        /// </summary>
        SymbolFont,

        /// <summary>
        ///  不知道哪个语言
        /// </summary>
        Unknown,
    }

 private static FontScheme GetFontScheme(SlidePart slidePart)
 {
    if (slidePart.ThemeOverridePart?.ThemeOverride?.FontScheme != null)
    {
        return slidePart.ThemeOverridePart.ThemeOverride.FontScheme;
    }

    var slideLayoutPart = slidePart.SlideLayoutPart;

    //从SlideLayout获取theme
    if (slideLayoutPart.ThemeOverridePart?.ThemeOverride?.FontScheme != null)
    {
        return slideLayoutPart.ThemeOverridePart.ThemeOverride.FontScheme;
    }

    var slideMasterPart = slideLayoutPart.SlideMasterPart;

    //从SlideMaster获取theme
    return slideMasterPart?.ThemePart?.Theme?.ThemeElements?.FontScheme;
 }

if (ThemeFontTypePattern.IsMatch(typeface))
{
    // 进入这个分支，字体是 +mn-ea 字体
    // 这个字体的意思里面 mn 表示 Body 字体
    // 而 mj 表示 Title 字体，也就是 Major 字体
    // 后续的 ea 和 lt 等表示采用东亚文字或拉丁文等
    // 此时需要获取字体主题
    var fontScheme = GetFontScheme(slidePart);
    FontCollectionType fontCollection;

    // mn 的 n 传入字符串是 +mn-ea 也就是第三个字符
    if (typeface[2] == 'n')
    {
        fontCollection = fontScheme.MinorFont;
    }
    else
    {
        fontCollection = fontScheme.MajorFont;
    }

    // 忽略代码
}

   FontLang fontLang = FontLang.Unknown;

    if (typeface.Contains("lt"))
    {
        fontLang = FontLang.LatinFont;
    }
    else if (typeface.Contains("cs"))
    {
        fontLang = FontLang.ComplexScriptFont;
    }
    else if (typeface.Contains("ea"))
    {
        fontLang = FontLang.EastAsianFont;
    }

        private static string GetScript(StringValue language)
        {
            if (language == "zh-CN")
            {
                return "Hans";
            }
            else if (language == "zh-Hant")
            {
                return "Hant";
            }

            // 默认值，当然，在 Office 里面的逻辑是十分多的，需要根据 [国家-地区字符串](https://docs.microsoft.com/zh-CN/cpp/c-runtime-library/country-region-strings?view=vs-2019 ) 文档写代码，只是这部分代码不是本文重点
            return "Hans";
        }

       private static string GetFontFromFontCollection(string scriptTag, FontLang themeTypefaceFontLang,
            FontCollectionType fontCollection)
        {
            if (fontCollection == null)
            {
                return string.Empty;
            }

            // 假定存在对应的语言的字体，那么获取对应的字体
            // 存放方式如
            /*
            <a:majorFont xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main">
                <a:latin typeface="Calibri Light" panose="020F0302020204030204" />
                <a:ea typeface="" />
                <a:cs typeface="" />
                <a:font script="Jpan" typeface="ＭＳ Ｐゴシック" />
                <a:font script="Hang" typeface="맑은 고딕" />
                <a:font script="Hans" typeface="宋体" />
            </a:majorFont>
            <a:minorFont xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main">
                <a:latin typeface="Calibri" panose="020F0502020204030204" />
                <a:ea typeface="" />
                <a:cs typeface="" />
                <a:font script="Jpan" typeface="ＭＳ Ｐゴシック" />
                <a:font script="Hang" typeface="맑은 고딕" />
                <a:font script="Hans" typeface="宋体" />
            </a:minorFont>
             */

            foreach (var font in fontCollection.Elements<SupplementalFont>())
            {
                // <a:font script="Hang" typeface="맑은 고딕" />
                if (string.Equals(font.Script, scriptTag, StringComparison.OrdinalIgnoreCase))
                {
                    return font.Typeface;
                }
            }

            // 忽略代码
        }

            // 也就是先尝试获取语言文化的，如果获取不到，就采用对应语言的
            TextFontType textFont = null;
            switch (themeTypefaceFontLang)
            {
                case FontLang.LatinFont:
                    textFont = fontCollection.LatinFont;
                    break;
                case FontLang.EastAsianFont:
                    textFont = fontCollection.EastAsianFont;
                    break;
                case FontLang.ComplexScriptFont:
                    textFont = fontCollection.ComplexScriptFont;
                    break;
                case FontLang.SymbolFont:
                    // 特别不处理，为什么？
                    // 在 fontCollection 是不存在的 SymbolFont 的
                    break;
                default:
                    throw new ArgumentOutOfRangeException(nameof(themeTypefaceFontLang), themeTypefaceFontLang, null);
            }

            var typeface = textFont?.Typeface?.Value;

            if (!string.IsNullOrEmpty(typeface))
            {
                return typeface;
            }

            Debug.Assert(false, "找不到字体");

            return null;