How can I add a simple horizontal line in Migradoc so as to separate the content above the line from the content below the line?
Paragraph 1
Paragraph 2
Paragraph 3
ETC
You can add a border to a paragraph or a table.
With respect to your sample, you could add a bottom border to paragraph 2 or add a top border to paragraph 3 or add a new paragraph between them and set either top or bottom border.