Convert XmlDocument to String

Assuming xmlDoc is an XmlDocument object whats wrong with xmlDoc.OuterXml?

return xmlDoc.OuterXml;

The OuterXml property returns a string version of the xml.

There aren't any quotes. It's just VS debugger. Try printing to the console or saving to a file and you'll see. As a side note: always dispose disposable objects:

using (var stringWriter = new StringWriter())
using (var xmlTextWriter = XmlWriter.Create(stringWriter))
{
    xmlDoc.WriteTo(xmlTextWriter);
    xmlTextWriter.Flush();
    return stringWriter.GetStringBuilder().ToString();
}