How to merge docx file using openxml SDK

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C#

MS-Word

OpenXML

Hi All,

I have created multiple diffrent docx file using open xml and when i am merging all formatting of every docx reset and merged with first doc formatting. Please help me when my docx file will merge then formatting and design should be remain of every pages.
My sniped code below:

using (WordprocessingDocument myDoc = WordprocessingDocument.Create(resultDoc, DocumentFormat.OpenXml.WordprocessingDocumentType.Document, true))
            {
                MainDocumentPart mainPart = myDoc.AddMainDocumentPart();
                new DocumentFormat.OpenXml.Wordprocessing.Document(new Body()).Save(mainPart);
                mainPart.Document.Body = new Body(new Paragraph());

                // Paragraph para = new Paragraph(new Run(new Break() { Type = BreakValues.Page }));
                // mainPart.Document.Body.InsertAfter(para, mainPart.Document.Body.LastChild);

                string altChunkId = "AltChunkId" + count;
                AlternativeFormatImportPart chunk = mainPart.AddAlternativeFormatImportPart(
                    AlternativeFormatImportPartType.WordprocessingML, altChunkId);
                using (FileStream fileStream = System.IO.File.Open(@"cover.docx", FileMode.Open))
                {
                    chunk.FeedData(fileStream);
                }

                chunk.FeedData(coverDoc);
                AltChunk altChunk = new AltChunk();
                altChunk.Id = altChunkId;
                mainPart.Document.Body.InsertAfter(altChunk, mainPart.Document.Body.Elements<Paragraph>().Last());
                mainPart.Document.Save();
                myDoc.Close();
                count = count + 1;
            }

What I have tried:

Open Xml Sdk, Word Docx file Merging