Adding a text watermark in C# with HTTPWebRequest

In this guide, we'll show you how to add text watermarks to your PDFs using C# and the HTTPWebRequest library.

When generating PDFs, you might want to add text watermarks to your documents for protection or branding purposes.

using System;
using System.Net;
using System.Text;
using System.IO;
using System.Threading.Tasks;

// You can get an API key at https://pdfshift.io
var apiKey = "sk_xxxxxxxxxxxx";

var request = (HttpWebRequest)WebRequest.Create("https://api.pdfshift.io/v3/convert/pdf");
request.Method = "POST";
request.ContentType = "application/json";
request.Headers.Add("X-API-Key", apiKey);

var payload = new
{
    source = "https://www.example.com",
    // Add text watermark
    watermark = new
    {
        text = "CONFIDENTIAL",
        opacity = 0.3,
        size = "20px",
        color = "#000000"
    }
};

var json = System.Text.Json.JsonSerializer.Serialize(payload);
byte[] data = Encoding.UTF8.GetBytes(json);
request.ContentLength = data.Length;

using (var stream = request.GetRequestStream())
{
    stream.Write(data, 0, data.Length);
}

try
{
    var response = (HttpWebResponse)request.GetResponse();
    
    // Handle errors:
    if (response.StatusCode >= HttpStatusCode.BadRequest)
    {
        throw new Exception($"Request failed with status code {response.StatusCode}");
    }

    using (var reader = new StreamReader(response.GetResponseStream()))
    {
        var result = reader.ReadToEnd();
        File.WriteAllText("result.pdf", result);
    }

    Console.WriteLine("The PDF document was generated and saved to result.pdf");
}
catch (WebException ex)
{
    Console.WriteLine($"Error: {ex.Message}");
}

This allows you to add textual protection to your documents with customizable text.

For further details on the watermark property and its usage, please refer to our dedicated documentation.

We hope this guide was helpful. If you have any questions or noticed any issues on the code above,
feel free to drop us a line.