使用OpenXML生成Word文档缩略图遇无效JPG及需取首页问题

我编写了如下代码，用于将Word文档（.docx）生成缩略图并以Base64字符串形式返回，但存在两个问题：

• 生成的结果并非有效的.jpg文件
• 无法仅提取文档的第一页作为缩略图

我认为OpenXML比Spire.doc更可靠，尝试的代码如下：

public string ExtractWordThumbnail(string wordFileBase64, string FileName)
{
    var outString = "";
    // Open the Word document
    byte[] byteArray = Convert.FromBase64String(wordFileBase64);
    using (MemoryStream stream = new MemoryStream()) { // Use decoded array as stream
        stream.Write(byteArray, 0, byteArray.Length);
        stream.Position = 0;
        using (WordprocessingDocument wordDoc = WordprocessingDocument.Open(stream, true))
        {
            if (wordDoc.ThumbnailPart == null)
            {
                // Add a new thumbnail part (JPEG in this case)
                var tPart = wordDoc.AddThumbnailPart(DocumentFormat.OpenXml.Packaging.ThumbnailPartType.Jpeg);
                // Feed the image data into the thumbnail part
                tPart.FeedData(stream);
            }

            var thumbStream = new MemoryStream();
            wordDoc.ThumbnailPart.GetStream().CopyTo(thumbStream);
            byte[] thumbBytes = thumbStream.ToArray();
            outString = Convert.ToBase64String(thumbBytes);
        }
    }
    return outString;
}

内容的提问来源于stack exchange，提问作者Gerard Lanphear