Simple thing: make the paragraph left-aligned, create two tabs (e.g. center-aligned in the middle, right-aligned at/near the right margin.
This code snippet creates two tabstops for a style (e.g. the Footer style):
Code:
style.ParagraphFormat.TabStops.ClearAll();
style.ParagraphFormat.TabStops.AddTabStop(Unit.FromMillimeter(80), TabAlignment.Center);
style.ParagraphFormat.TabStops.AddTabStop(Unit.FromMillimeter(158), TabAlignment.Right);
Add the left-aligned text, then "paragraph.AddTab();" and the centered text, then "paragraph.AddTab();" and the right-aligned text.