How to send a PDF file to a WhatsApp group in C# (.NET) using Visual Studio 2019

This article shows you how to send a document (e.g. a PDF file, an MP4 file, a WAV file, etc.) document to a WhatsApp group in Microsoft’s .NET language: C# using Visual Studio 2019.

If you are using Visual Studio 2022, please read this tutorial instead.

To send a PDF document to a WhatsApp group in C#, do this:

First, learn how to send a simple text message to a group on the official site.
With the above knowledge, you can now download our sample code.

Locate the file cs/send-pdf-group.cs.

	using System;
	using System.Net;
	using System.Web.Script.Serialization; // requires the reference 'System.Web.Extensions'
	using System.IO;
	using System.Text;

	class WaPdfGroupSender
	{
	// TODO: Replace the following with your gateway instance ID, client ID and secret!
	private static string INSTANCE_ID = "YOUR_INSTANCE_ID";
	private static string CLIENT_ID = "YOUR_CLIENT_ID_HERE";
	private static string CLIENT_SECRET = "YOUR_CLIENT_SECRET_HERE";

	private static string DOCUMENT_SINGLE_API_URL = "http://api.whatsmate.net/v3/whatsapp/group/document/message/" + INSTANCE_ID;

	static void Main(string[] args)
	{
	WaPdfGroupSender groupDocSender = new WaPdfGroupSender();
	// TODO: Put down the unique name of your group here
	string group = "YOUR UNIQUE GROUP NAME HERE";
	// TODO: Remember to copy the JPG from ..\assets to the TEMP directory!
	string base64Content = convertFileToBase64("C:\\TEMP\\subwaymap.pdf");
	string fn = "anyname.pdf";
	string caption = "You will find the map handy.";

	groupDocSender.sendGroupDocument(group, base64Content, fn, caption);

	Console.WriteLine("Press Enter to exit.");
	Console.ReadLine();
	}

	// http://stackoverflow.com/questions/25919387/c-sharp-converting-file-into-base64string-and-back-again
	static public string convertFileToBase64(string fullPathToDoc)
	{
	Byte[] bytes = File.ReadAllBytes(fullPathToDoc);
	String base64Encoded = Convert.ToBase64String(bytes);
	return base64Encoded;
	}

	public bool sendGroupDocument(string group, string base64Content, string fn, string caption)
	{
	bool success = true;

	try
	{
	using (WebClient client = new WebClient())
	{
	client.Headers[HttpRequestHeader.ContentType] = "application/json";
	client.Headers["X-WM-CLIENT-ID"] = CLIENT_ID;
	client.Headers["X-WM-CLIENT-SECRET"] = CLIENT_SECRET;

	GroupDocumentPayload payloadObj = new GroupDocumentPayload() { group_name = group, document = base64Content, filename = fn, caption = caption};
	string postData = (new JavaScriptSerializer()).Serialize(payloadObj);

	client.Encoding = Encoding.UTF8;
	string response = client.UploadString(DOCUMENT_SINGLE_API_URL, postData);
	Console.WriteLine(response);
	}
	}
	catch (WebException webEx)
	{
	Console.WriteLine(((HttpWebResponse)webEx.Response).StatusCode);
	Stream stream = ((HttpWebResponse)webEx.Response).GetResponseStream();
	StreamReader reader = new StreamReader(stream);
	String body = reader.ReadToEnd();
	Console.WriteLine(body);
	success = false;
	}

	return success;
	}

	public class GroupDocumentPayload
	{
	public string group_name { get; set; }
	public string document { get; set; }
	public string filename { get; set; }
	public string caption { get; set; }
	}

	}

view raw send-pdf-group.cs hosted with ❤ by GitHub

Study the C# source code and customize the TODO/FIXME lines.
- Among other things, you must name your group creatively. Otherwise, the group may not receive the message.
Run the C# program in Visual Studio to send your group the first PDF file!

Happy coding :)