// Load Word documents to be merged
Document doc1 = new Document("sample1.docx");
Document doc2 = new Document("sample4.docx");

// Merge documents keeping source file's formatting
doc1.AppendDocument(doc2, ImportFormatMode.KeepSourceFormatting);

// Save merged document as DOCX file
doc1.Save("merged.docx", SaveFormat.Docx);