HTML to PDF C#

Take your ConvertAPI C# integrations to the next level with advanced techniques for real-world, production-grade document conversion workflows.

These advanced patterns help you build robust, scalable, and efficient HTML to PDF pipelines in your .NET applications while maintaining flexibility and control over your document workflows.

Convert a Remote HTML File

The following C# example demonstrates how to convert a HTML file hosted online (accessible via a public URL) directly to PDF using ConvertAPI. This is useful when your documents are already stored on cloud storage (S3, Azure Blob, etc.) and you want to convert them without downloading locally first.

In this example:

• No local download needed before conversion.
• The HTML file is fetched from the provided URL.
• ConvertAPI converts it to PDF and saves it to a temporary folder on your server or local machine.
• Ideal for server-side processing pipelines and automated workflows.

var convertApi = new ConvertApi("api_key");
var sourceFile = new Uri("https://cdn.convertapi.com/public/files/demo.html");

Console.WriteLine($"Converting online {sourceFile} document to PDF...");

var htmlToPdfResult = await convertApi.ConvertAsync("html", "pdf", new ConvertApiFileParam(sourceFile));
var outputFileName = htmlToPdfResult.Files[0];
var fileInfo = await outputFileName.SaveFileAsync(Path.Combine(Path.GetTempPath(), outputFileName.FileName));

Console.WriteLine("The PDF result saved to " + fileInfo);

Convert a HTML File Stream to PDF and Receive a File Stream

This C# example demonstrates how to convert a HTML file provided as a stream directly to PDF using ConvertAPI and receive the converted PDF as a stream without writing to disk. This is ideal for in-memory processing in ASP.NET APIs, serverless functions, or pipeline services where you need to handle documents securely and efficiently.

In this example:

• You pass a HTML file stream (html_stream) with a filename hint to ConvertAPI.
• ConvertAPI converts the document to PDF without saving intermediate files.
• The converted PDF is returned as a stream (outputStream) for direct processing, returning to clients, or further manipulation in your pipeline.
• Ideal for secure, diskless document conversion workflows.

var conversionResult = await convertApi.ConvertAsync("html", "pdf",
new ConvertApiFileParam(html_stream, "test.html")
);
var outputStream = await conversionResult.Files.First().FileStreamAsync();

Console.Write(new StreamReader(outputStream).ReadToEnd());
Console.WriteLine("End of file stream.");

Handling Exceptions During HTML to PDF Conversion

This C# example shows how to handle exceptions when converting a HTML file to PDF using ConvertAPI. By catching ConvertApiException, you can access detailed error information, making it easier to debug issues such as invalid API tokens, unsupported file formats, or conversion errors in your workflow.

In this example:

• A try-catch block safely wraps the HTML to PDF conversion.
• If the API call fails, ConvertApiException provides the HTTP status code and API response details for clear diagnostics.
• This approach ensures your application can handle errors gracefully, log issues, and respond with meaningful messages to users or calling services.

try
{
    var convertApi = new ConvertApi("api_token");
    const string sourceFile = @"..\..\..\TestFiles\test.html";

    var convert = await convertApi.ConvertAsync("html", "pdf",
    new ConvertApiFileParam(sourceFile));
}
//Catch exceptions and write details
catch (ConvertApiException e)
{
    Console.WriteLine("Status Code: " + e.StatusCode);
    Console.WriteLine("Response: " + e.Response);
}