Microsoft Word Interop performance issue

I have a winform program which loads Microsoft Word and performs some basic editing (find & replace), as well as some autosaving.

It loads an existing word template, which again is basic text.

The code for the interop is;

 try
        {
            // Is Word running?
            WordApp = System.Runtime.InteropServices.Marshal.GetActiveObject("Word.Application") as Microsoft.Office.Interop.Word.Application;
            WordApp.Visible = true;
            return WordApp;
        }
catch (COMException ce)
        {
            WordApp = null;
            if (ce.ErrorCode == unchecked((int)0x800401E3))

                WordApp = new Microsoft.Office.Interop.Word.Application();

            WordApp.Visible = true;
            return WordApp;
        }

Once the document is open, the user types what they need to but it has been noted that after a page or so of text, the performance really slows. There is an increasing lag on the users typing.

I thought initially it was due to some issues with the find/replace code so I have commented out everything apart from the code for loading the template;

            WordApp = WordEdit.GetWord(); //Class & Method calling interop code
        WordApp.Documents.Add(AppDomain.CurrentDomain.BaseDirectory + "\\Templates\\" + DocType + ".dot");

        //set Active Document
        WordDoc = WordApp.ActiveDocument;

The performance is still as poor.

I then thought to release the COM and set things to null, but again this didn't have any effect.

     System.Runtime.InteropServices.Marshal.ReleaseComObject(WordApp);
        WordApp = null;
        WordDoc = null;

I then thought maybe my app is causing the system in general to slow down. If I quit the application but continue to use the Word application it load, the performance is still slow. If I start a fresh Word application (manually) this works perfectly. So it has something to do with the way my application is loading word. My application does not have any impact on system resources, and is currently set to do nothing other than load the template.

Is there either a different way get hold of Word (a different way to use interop) or a way to improve performance?