Copying contents of Word doc and paste into another c#
object docStart = worddocpromo.Content.End - 1;
object docEnd = worddocpromo.Content.End;

object start = SubDoc.Content.Start;
object end = SubDoc.Content.End;

SubDoc.Range(ref start, ref end).Copy();
Microsoft.Office.Interop.Word.Range rng = worddocpromo.Range(ref docStart, ref docEnd);
rng.Paste();