HTML to PDF in C#

One POST, a PDF back. No headless browser to install, no Chromium to keep patched, no fonts to install on the box — the render happens on a warm browser that is already running.

Render HTML to a PDF

using System.Net.Http.Json;

var client = new HttpClient { Timeout = TimeSpan.FromSeconds(60) };
client.DefaultRequestHeaders.Authorization =
    new("Bearer", Environment.GetEnvironmentVariable("PDFCRAFT_API_KEY"));

var response = await client.PostAsJsonAsync("https://api.pdfcraft.dev/v1/render", new
{
    html = "<h1>Invoice 1042</h1>",
    options = new { printBackground = true, margin = new { top = "20mm" } }
});
response.EnsureSuccessStatusCode();

await using var file = File.Create("invoice.pdf");
await response.Content.CopyToAsync(file);

Read a PDF back as JSON

The same key works for extraction. Send a PDF, name the fields you want by the label printed on the page, and get them back with the raw text, a coerced value, a confidence and a bounding box.

var encoded = Convert.ToBase64String(await File.ReadAllBytesAsync("statement.pdf"));

var response = await client.PostAsJsonAsync("https://api.pdfcraft.dev/v1/extract", new
{
    file = encoded,
    schema = new Dictionary<string, string>
    {
        ["account_number"] = "string",
        ["closing_balance"] = "currency"
    },
    options = new { rows_as_objects = true }
});

var body = await response.Content.ReadFromJsonAsync<JsonElement>();
Console.WriteLine(body.GetProperty("fields").GetProperty("closing_balance").GetProperty("value"));

What bites in C#

Reuse one HttpClient for the life of the process. A `using var client = new HttpClient()` per call exhausts sockets under load — the classic .NET failure mode, and it only appears in production.
`CopyToAsync` to a FileStream rather than `ReadAsByteArrayAsync`, so a large PDF never lands on the large object heap.
System.Text.Json serialises anonymous objects camelCase by default, which matches the API. If you have configured a different policy globally, the option names will not match and you will get a 400.

Errors are one shape

Every failure is {"error":{"code","message","docs_url"}} with a stable code, so you can switch on error.code rather than parsing prose. The two worth handling explicitly are rate_limited — honour Retry-After — and render_failed, which means your HTML broke rather than ours did.

The same thing in another language

Or try it with no code at all in the playground. A free key is 100 renders a month.