C# / .NET HTML to PDF API guide

Use C# and HttpClient to generate PDFs from ASP.NET Core applications, services, workers, or console apps.

cURL PHP Node.js Python Ruby Java C# / .NET Go

EndpointPOST https://api.html2pdf.app/v1/generate

AuthenticationX-API-Key: <your-api-key>

Overview

Post JSON with the built-in .NET HTTP APIs, validate the response, and save or return the generated PDF as binary data.

The API accepts a JSON request body. Send either a public URL or inline HTML in the required html parameter. For normal synchronous conversions, the response body is the generated PDF and should be saved as binary data.

Requirements

.NET 8 or newer
An html2pdf.app API key stored in configuration or the environment
A server-side application, worker, or trusted console app

Quick start

Replace <your-api-key> or the environment variable with your html2pdf.app API key, then run the example from a trusted backend environment.

Send a public URL to the API, check the HTTP response, and save the returned bytes to document.pdf.

using System.Net.Http.Json;

const string endpoint = "https://api.html2pdf.app/v1/generate";

var apiKey = Environment.GetEnvironmentVariable("HTML2PDF_API_KEY")
    ?? throw new InvalidOperationException("HTML2PDF_API_KEY is not set.");

using var client = new HttpClient();
client.DefaultRequestHeaders.Add("X-API-Key", apiKey);

using var response = await client.PostAsJsonAsync(endpoint, new
{
    html = "https://www.example.com",
});

if (!response.IsSuccessStatusCode)
{
    var error = await response.Content.ReadAsStringAsync();
    throw new HttpRequestException("PDF generation failed: " + error);
}

var pdf = await response.Content.ReadAsByteArrayAsync();
await File.WriteAllBytesAsync("document.pdf", pdf);

C# / .NET examples

These examples cover the next common production flows: generating from inline HTML with options and queuing a callback job.

1. Return a PDF from ASP.NET Core

Generate an invoice with layout options and return it directly from a minimal API endpoint.

using System.Net.Http.Json;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddHttpClient();

var app = builder.Build();

app.MapGet("/invoice.pdf", async (
    IHttpClientFactory clientFactory,
    IConfiguration configuration) =>
{
    var apiKey = configuration["HTML2PDF_API_KEY"]
        ?? throw new InvalidOperationException("HTML2PDF_API_KEY is not set.");

    var client = clientFactory.CreateClient();
    client.DefaultRequestHeaders.Add("X-API-Key", apiKey);

    using var response = await client.PostAsJsonAsync("https://api.html2pdf.app/v1/generate", new
    {
        html = "<h1>Invoice</h1><p>Total: $240.00</p>",
        format = "A4",
        media = "print",
        marginTop = 40,
        marginRight = 32,
        marginBottom = 40,
        marginLeft = 32,
        filename = "invoice.pdf",
    });

    IResult result;

    if (!response.IsSuccessStatusCode)
    {
        var error = await response.Content.ReadAsStringAsync();
        result = Results.Problem("PDF generation failed: " + error);
    }
    else
    {
        var pdf = await response.Content.ReadAsByteArrayAsync();
        result = Results.File(pdf, "application/pdf", "invoice.pdf");
    }

    return result;
});

app.Run();

2. Queue an asynchronous conversion

Provide callback details when the generated PDF should be delivered to a webhook instead of returned immediately.

using System.Net.Http.Json;

const string endpoint = "https://api.html2pdf.app/v1/generate";

var apiKey = Environment.GetEnvironmentVariable("HTML2PDF_API_KEY")
    ?? throw new InvalidOperationException("HTML2PDF_API_KEY is not set.");

using var client = new HttpClient();
client.DefaultRequestHeaders.Add("X-API-Key", apiKey);

using var response = await client.PostAsJsonAsync(endpoint, new
{
    html = "https://www.example.com/report",
    callBackUrl = "https://your-app.com/webhooks/html2pdf",
    state = "report-1042",
});

if (!response.IsSuccessStatusCode)
{
    var error = await response.Content.ReadAsStringAsync();
    throw new HttpRequestException("Unable to queue PDF conversion: " + error);
}

Request options

Most integrations start with html and then add options as the document design becomes more specific.

html is required and accepts a public URL or raw HTML.
format, landscape, width, and height control page size.
marginTop, marginRight, marginBottom, and marginLeft control whitespace around the rendered page.
media selects screen or print CSS rendering.
callBackUrl switches the request to asynchronous generation and sends the completed PDF to your webhook.

See the full API parameter reference for every supported field.

Troubleshooting

Reuse HttpClient instances or IHttpClientFactory in long-running applications.
Read synchronous responses as bytes so the PDF is never treated as text.
Check the HTTP status before saving or returning the response as a PDF.

If the generated document is blank or missing styles, first confirm that the source URL is public and that required CSS, fonts, and images are reachable by the rendering service.

More language guides

cURL

Use cURL to test the HTML to PDF API from a terminal, shell script, CI job, or backend task.

PHP

Use PHP and cURL to generate PDFs from Laravel, Symfony, WordPress, or plain PHP backends.

Node.js

Use native fetch in Node.js to create PDFs from API routes, workers, queues, or command line scripts.

Python

Use Python requests to generate PDFs from Django, Flask, FastAPI, notebooks, or batch scripts.

Ruby

Use Ruby standard library HTTP clients to generate PDFs from Rails, Sidekiq, Rake tasks, or scripts.

Java

Use the Java HttpClient API to generate PDFs from Spring Boot services, jobs, or CLI tools.

Use Go standard library HTTP clients to generate PDFs from services, CLIs, workers, or cron jobs.