RichTextBox richTextBox = new RichTextBox();
// 假设已经有内容被添加到RichTextBox中

foreach (Block block in richTextBox.Document.Blocks)
{
    if (block is Paragraph paragraph)
    {
        foreach (Inline inline in paragraph.Inlines)
        {
            if (inline is Run run)
            {
                FormattedText formattedText = new FormattedText(
                    run.Text,
                    CultureInfo.CurrentCulture,
                    FlowDirection.LeftToRight,
                    new Typeface(richTextBox.FontFamily, richTextBox.FontStyle, richTextBox.FontWeight, richTextBox.FontStretch),
                    richTextBox.FontSize,
                    Brushes.Black);

                double lineHeight = formattedText.Height;
                // 在这里可以使用lineHeight，即为段落行高度
            }
        }
    }
}

Paragraph paragraph = new Paragraph();
paragraph.LineHeight = 20; // 设置行高度为20

// 将段落添加到RichTextBox中
richTextBox.Document.Blocks.Add(paragraph);