Add Signature while replying using Selection c# vsto addin

I am new to C# VSTO Add-In development and am trying to add a signature at the cursor's location. However, I'm unable to insert HTML and can only add plain text. How can I append HTML instead?

I tried the code below and was able to add text. How can I append HTML instead?

// Get the active Inspector (email editor)
Outlook.Inspector inspector = outlookApp.ActiveInspector();

if (inspector != null && inspector.CurrentItem is Outlook.MailItem mailItem)
{
    // Get the Word editor for the email
    Document wordDocument = inspector.WordEditor as Document;

    if (wordDocument != null)
    {
        // Access the current selection (cursor position)
        Selection selection = wordDocument.Application.Selection;

        if (selection != null)
        {
            // Insert HTML at the current selection (cursor position)
            Range range = selection.Range;
            selection.TypeText(signature);
            // Set the range's HTML format to preserve HTML tags
            range.FormattedText = wordDocument.Application.Selection.FormattedText;
            // Set the email's HTML body to include the new HTML content
            //mailItem.HTMLBody = mailItem.HTMLBody.Insert(mailItem.HTMLBody.Length, "Ram");
            return "NOTREQUIRED";
        }

    }
}

Then tried below code,

//Insert the HTML content at the current cursor position
 selection.Range.InsertAfter(htmlContent);

HTML is not being added in this location. I'm not sure what I did wrong. Can you help me figure it out?