index.aspx.cs

// create the helper object to pass the required parameters
// as a JSON object
MailMergeRequestObject requestObject = new MailMergeRequestObject();

// load the data as XML
XmlDocument doc = new XmlDocument();
doc.Load(Server.MapPath("sample_db.xml"));

// the Web API expects the data as a JSON object
// 'JsonConvert' converts the XML to the required JSON format
string jsonText = JsonConvert.SerializeXmlNode(doc);

// fill the helper object with the data and the template
requestObject.Data = jsonText;
requestObject.Template = System.IO.File.ReadAllBytes(
	Server.MapPath("template.tx"));

// new helper object of type 'Results' that keeps
// the resulting document as a byte[]
Results results;
string sFormat = DropDownList1.SelectedValue;

// create a new WebClient object
using (var client = new WebClient())
{
	// set the headers to send and accept JSON
	client.Headers[HttpRequestHeader.ContentType] = "application/json";
	client.Headers[HttpRequestHeader.Accept] = "application/json";
	// upload the helper object as a JSON string
	string result = client.UploadString(
		"http://localhost:13012/api/Merge?format=" + sFormat,
		"POST",
		JsonConvert.SerializeObject(requestObject));

	// deserialize and convert the returned JSON object
	// to the helper object 'Results'
	results = (Results)JsonConvert.DeserializeObject(result, typeof(Results));
}

// save the resulting document as a file
// and create a hyperlink that points to the new file
System.IO.File.WriteAllBytes(
	Server.MapPath("results." + sFormat), results.Document);
Response.Write("Download generated document <a href=\"results." + 
	sFormat.ToLower() + "\">here</a> (results." +
	sFormat.ToLower() + ").");