这段代码应该将现有文档的所有部分复制到新文档中.

This piece of code should copy all parts from an existing document to a new one.

using (var mainDoc = WordprocessingDocument.Open(@"c:\sourcedoc.docx", false))
using (var resultDoc = WordprocessingDocument.Create(@"c:\newdoc.docx",
  WordprocessingDocumentType.Document))
{
  // copy parts from source document to new document
  foreach (var part in mainDoc.Parts)
    resultDoc.AddPart(part.OpenXmlPart, part.RelationshipId);
  // perform replacements in resultDoc.MainDocumentPart
  // ...
}