Convert a page behind a login to PDF in C#

Build it step by step.

1. 1Install the NuGet packages

   SelectPdf.Universal is the library. The native package carries the Chromium engine for one platform: add the one for the platform you run on.

   Windows x64 Linux x64 Linux ARM64 macOS · Apple Silicon
   terminal COPY

   dotnet add package SelectPdf.Universal
   dotnet add package SelectPdf.Universal.Native.win-x64

   terminal COPY

   dotnet add package SelectPdf.Universal
   dotnet add package SelectPdf.Universal.Native.linux-x64

   terminal COPY

   dotnet add package SelectPdf.Universal
   dotnet add package SelectPdf.Universal.Native.linux-arm64

   terminal COPY

   dotnet add package SelectPdf.Universal
   dotnet add package SelectPdf.Universal.Native.osx-arm64

2. 2Create a web app

   Any .NET 8 or .NET 10 project works. To follow along, create an empty ASP.NET Core app, run the install commands above inside its folder, then replace Program.cs with the code below.

   terminal COPY

   dotnet new web -n PdfSample
   cd PdfSample

3. 3Import the namespace

   Program.cs · lines 1–1 COPY

   using SelectPdf.Universal;

   The project is created with dotnet new web, which brings in ASP.NET Core for the stand-in site; the converter is in SelectPdf.Universal.

4. 4A protected page to convert

   Program.cs · lines 3–12 COPY

   // 1. A stand-in for your site: a report page that needs a bearer token.
   // It runs on localhost so the sample works anywhere.
   WebApplication app = WebApplication.Create();
   app.Urls.Add("http://127.0.0.1:0"); // any free port
   app.MapGet("/report", (HttpRequest request) =>
       request.Headers.Authorization == "Bearer s3cret-token"
           ? Results.Content("<h1>Sales report</h1><p>Signed in: the converter sent the token.</p>", "text/html")
           : Results.Content("<h1>Please sign in</h1>", "text/html", statusCode: 401));
   await app.StartAsync();
   string site = app.Urls.First();

   A small ASP.NET Core app on localhost plays the part of your site: /report answers with the report only when the request carries Authorization: Bearer s3cret-token, and with "Please sign in" otherwise. Port 0 picks any free port; app.Urls gives the address it got. In your application, convert your real URL and skip this step.

5. 5Send the Authorization header

   Program.cs · lines 14–16 COPY

   // 2. Send the Authorization header with every request the converter makes.
   HtmlToPdf converter = new HtmlToPdf();
   converter.Options.HttpHeaders.Add("Authorization", "Bearer s3cret-token");

   Options.HttpHeaders adds headers to the requests the converter makes. With the bearer token in Authorization, the page sees the same request your API client or signed-in browser would send.

6. 6Convert the protected page

   Program.cs · lines 18–21 COPY

   // 3. Convert the protected page and save it.
   PdfDocument doc = converter.ConvertUrl($"{site}/report");
   doc.Save("report.pdf");
   doc.Close();

   ConvertUrl loads the page with the header and renders it, so report.pdf holds the sales report, not the sign-in page.

7. 7Stop the stand-in site

   Program.cs · lines 23–23 COPY

   await app.StopAsync();

   StopAsync shuts the local site down when the conversion is done.

8. 8Run it

   terminal COPY

   dotnet run

   The request returns report.pdf. Without a license key, every page carries a trial watermark; set GlobalProperties.LicenseKey before the first conversion to remove it.

The complete Program.cs.

This is the exact file our samples pipeline compiled and ran on Linux ARM64 and Linux x64 and macOS ARM64 and Windows x64 to produce the output on this page.

using SelectPdf.Universal;

// 1. A stand-in for your site: a report page that needs a bearer token.
// It runs on localhost so the sample works anywhere.
WebApplication app = WebApplication.Create();
app.Urls.Add("http://127.0.0.1:0"); // any free port
app.MapGet("/report", (HttpRequest request) =>
    request.Headers.Authorization == "Bearer s3cret-token"
        ? Results.Content("<h1>Sales report</h1><p>Signed in: the converter sent the token.</p>", "text/html")
        : Results.Content("<h1>Please sign in</h1>", "text/html", statusCode: 401));
await app.StartAsync();
string site = app.Urls.First();

// 2. Send the Authorization header with every request the converter makes.
HtmlToPdf converter = new HtmlToPdf();
converter.Options.HttpHeaders.Add("Authorization", "Bearer s3cret-token");

// 3. Convert the protected page and save it.
PdfDocument doc = converter.ConvertUrl($"{site}/report");
doc.Save("report.pdf");
doc.Close();

await app.StopAsync();

Open the project on GitHub → this program and the variations below, ready to dotnet run

The PDF it produces.

Variations you will need next.

Each variation is a separate file in the same project, compiled and run with the program above.

Send the session cookie of a signed-in user

Sites with cookie sign-in, such as ASP.NET Core cookie authentication, recognize the user by a cookie. Options.HttpCookies.Add(name, value) sends it with the conversion. In a web app, read the cookie from the current request, for example Request.Cookies[".AspNetCore.Cookies"], so the PDF shows what that user sees.

using SelectPdf.Universal;

static class CookieAuth
{
    public static async Task Run()
    {
        // a page that needs the session cookie of a signed-in user
        WebApplication app = WebApplication.Create();
        app.Urls.Add("http://127.0.0.1:0");
        app.MapGet("/orders", (HttpRequest request) =>
            request.Cookies["session"] == "user-42-session"
                ? Results.Content("<h1>My orders</h1><p>Signed in with the session cookie.</p>", "text/html")
                : Results.Redirect("/login"));
        await app.StartAsync();

        // in a web app, read the cookie from the current request:
        // Request.Cookies[".AspNetCore.Cookies"]
        HtmlToPdf converter = new HtmlToPdf();
        converter.Options.HttpCookies.Add("session", "user-42-session");
        PdfDocument doc = converter.ConvertUrl($"{app.Urls.First()}/orders");
        doc.Save("orders.pdf");
        doc.Close();

        await app.StopAsync();
    }
}

HTTP Basic authentication

When the server asks for HTTP credentials (the browser's login dialog), Options.Authentication.Username and Password answer the challenge. The same options supply credentials for Integrated Windows Authentication when the current user's are not enough.

using System.Text;
using SelectPdf.Universal;

static class BasicAuth
{
    public static async Task Run()
    {
        // a page behind HTTP Basic authentication
        string expected = "Basic " + Convert.ToBase64String(Encoding.UTF8.GetBytes("reports:pa55word"));
        WebApplication app = WebApplication.Create();
        app.Urls.Add("http://127.0.0.1:0");
        app.MapGet("/status", (HttpRequest request, HttpResponse response) =>
        {
            if (request.Headers.Authorization == expected)
                return Results.Content("<h1>System status</h1><p>Signed in with HTTP authentication.</p>", "text/html");
            response.Headers.WWWAuthenticate = "Basic realm=\"reports\"";
            return Results.Unauthorized();
        });
        await app.StartAsync();

        // the converter answers the login challenge with these credentials
        HtmlToPdf converter = new HtmlToPdf();
        converter.Options.Authentication.Username = "reports";
        converter.Options.Authentication.Password = "pa55word";
        PdfDocument doc = converter.ConvertUrl($"{app.Urls.First()}/status");
        doc.Save("status.pdf");
        doc.Close();

        await app.StopAsync();
    }
}

Sign in through the site's login form

Options.LoginOptions opens LoginPage, types the user name and password into the fields matched by the CSS selectors, clicks the submit button and then converts the URL, with the cookie the login set. DelayBefore and DelayAfter (milliseconds) give slow login pages time to load and to redirect.

using SelectPdf.Universal;

static class LoginForm
{
    public static async Task Run()
    {
        // a site with its own login form; the dashboard needs the cookie it sets
        WebApplication app = WebApplication.Create();
        app.Urls.Add("http://127.0.0.1:0");
        app.MapGet("/login", () => Results.Content("""
            <form method="post" action="/login">
              <input id="user" name="user"> <input id="pass" name="pass" type="password">
              <button id="sign-in" type="submit">Sign in</button>
            </form>
            """, "text/html"));
        app.MapPost("/login", (HttpContext context) =>
        {
            IFormCollection form = context.Request.Form;
            if (form["user"] != "anna" || form["pass"] != "pa55word") return Results.Redirect("/login");
            context.Response.Cookies.Append("session", "anna-session");
            return Results.Redirect("/dashboard");
        });
        app.MapGet("/dashboard", (HttpRequest request) =>
            request.Cookies["session"] == "anna-session"
                ? Results.Content("<h1>Dashboard</h1><p>Signed in through the login form.</p>", "text/html")
                : Results.Redirect("/login"));
        await app.StartAsync();
        string site = app.Urls.First();

        // the converter opens the login page, fills in the form and submits it first
        HtmlToPdf converter = new HtmlToPdf();
        converter.Options.LoginOptions.LoginPage = $"{site}/login";
        converter.Options.LoginOptions.UsernameFieldSelector = "#user";
        converter.Options.LoginOptions.PasswordFieldSelector = "#pass";
        converter.Options.LoginOptions.SubmitButtonSelector = "#sign-in";
        converter.Options.LoginOptions.Username = "anna";
        converter.Options.LoginOptions.Password = "pa55word";
        PdfDocument doc = converter.ConvertUrl($"{site}/dashboard");
        doc.Save("dashboard.pdf");
        doc.Close();

        await app.StopAsync();
    }
}

Common problems and fixes.

Good to know.

• HtmlToPdfOptions.HttpHeaders sends additional HTTP headers to the page that is converted. Source
• HtmlToPdfOptions.HttpCookies sends cookies; the converter issues its own request, so it is anonymous unless the authentication cookie is passed to it. Source
• For HTTP authentication, set Options.Authentication.Username and Password; the converter uses them to log in and access the page. Source
• LoginOptions gets past a login page given its URL, the CSS selectors of the user name and password fields and of the submit button, and the credentials. Source
• The converter keeps its HTTP cache between conversions by default, keyed by address; for pages converted on behalf of different users, set HttpCache to HttpCacheMode.Clear. Source