Finding and replacing text in memystream in C # .NET.

I have uploaded a memystream with a text document and I want to be able to modify certain text in the memystream and save it back to the text document, for example search and replace functionality. Please help me with this because I don't want to use Word Interop libraries. I have a code to load and save a document, see below. The problem is that if I convert the storage device to a string and use the string replacement method, when I save the string, all formatting inside the word document is lost and when I open the document, all it shows are black boxes all over the place.

        private void ReplaceInFile(string filePath, string searchText, string replaceText)
    {
        byte[] inputFile = File.ReadAllBytes(filePath);
        MemoryStream memory = new MemoryStream(inputFile);

        byte[] data = memory.ToArray();

        string pathStr = Request.PhysicalApplicationPath + "\\Docs\\OutputDocument.doc";
        FileInfo wordFile = new FileInfo(pathStr);
        FileStream fileStream = wordFile.Open(FileMode.Create, FileAccess.Write, FileShare.None);

        fileStream.Write(data, 0, data.Length);

        fileStream.Close();

        memory.Close();
    }

      

        
        
        
      

    

I copied the code from the sample code online. So this is why memystream was used as I had no idea how to do it. My problem is that the company I work with doesn't want to use the word interop as they sometimes found that the word could display popup dialogs on randomness, which prevents the coded functionality from executing. This is why I want to look at ways to achieve the merge functionality, but programmatically. I did very similar to what I want to do here many years ago, but not in C # in Delphi and I tend to lose the code. So if anyone can shed some light on this, I would be grateful.