How to align text in bottom in a flowdocument? [wpf, C#]

I have a paragraph to add inline text and loading it into a flowdocument to render richtext with image in RichTextBox. below is my code.

var flowDocument = new FlowDocument();
Paragraph paragraph = new Paragraph();
paragraph.Inlines.Add(AppendFormat(grid, richText.GetFont(richText.Text.IndexOf(run.Text)), run));
paragraph.TextAlignment = TextAlignment.Right;
flowDocument.Blocks.Add(paragraph);

The problem I'm facing is TextAlignment for paragraph and flowdocument are has option for horizontal alignments alone. How to align the content based on vertical alignment?

Thanks in advance,

Arulpriya R.