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Converting HTML to PDF or Image in C# Using wkhtmltopdf

Here's a guide on generating PDF or image files from HTML using wkhtmltopdf in C#. This method is widely used due to wkhtmltopdf’s capability to handle complex HTML, CSS, and even JavaScript, producing high-quality PDFs or images.

1. Setting Up wkhtmltopdf

wkhtmltopdf is a command-line tool that converts HTML to PDF and images using Webkit. Before integrating it with C#, you’ll need to.

  • Download wkhtmltopdf from the official site.
  • Install it on your machine and note the installation path (usually C:\Program Files\wkhtmltopdf on Windows).
    Installation path

2. Creating a C# Wrapper Engine for wkhtmltopdf

In C#, you can call wkhtmltopdf using System.Diagnostics.Process to execute command-line arguments. Here’s a basic implementation.

  • Interface for Convert Items
  • Process Path will be exe path of Engine
  • Engine Type will be 1-> PDF Engine, 2-> Image Engine; If we need more we can add future. 
     public interface IConverterWebKitEngine
{
    string ProcessPath { get; }
    int EngineType { get; }
    bool ConvertContent(string inputPath, string outputPath);
}
  • PDF Engine Implementation. 
     public class PDFConsoleConverter : IConverterWebKitEngine
{
    private readonly ILogger<PDFConsoleConverter> _logger;
    private readonly IWebHostEnvironment _hostingEnvironment;
    public string ProcessPath { get; }
    public int EngineType { get; } = 1;

    public PDFConsoleConverter(ILogger<PDFConsoleConverter> logger, IWebHostEnvironment hostingEnvironment)
    {
        _logger = logger;
        _hostingEnvironment = hostingEnvironment;
        ProcessPath = _hostingEnvironment.WebRootPath + @$"\Tool\wkhtmltopdf.exe";
    }

    public bool ConvertContent(string inputPath, string outputPath)
    {
        try
        {
            var ticks = DateTime.UtcNow.Ticks;
            string switches = "";

            #region headers
            switches += "--header-center wkhtmltopdf ";
            switches += "--header-line ";
            switches += "--header-spacing 5 ";
            #endregion

            #region general
            switches += "--print-media-type ";
            switches += "--margin-top 40mm --margin-bottom 10mm --margin-right 10mm --margin-left 10mm ";
            switches += "--page-size A4 ";
            #endregion

            #region footer
            switches += "--footer-line ";
            switches += "--footer-center \"[page] of [topage]\" ";
            #endregion

            string processPdfpath = ProcessPath;

            Process process = new Process();
            process.StartInfo.UseShellExecute = true;
            process.StartInfo.FileName = processPdfpath;
            process.StartInfo.Arguments = $"{switches} \"{inputPath}\" \"{outputPath}\" ";
            process.Start();
        }
        catch (Exception ex)
        {
            _logger.LogCritical(ex.Message);
            return true;
        }
        return true;
    }
}
  • Image Engine Implementation. 
     public class ImageConsoleConverter : IConverterWebKitEngine
{
    private readonly ILogger<ImageConsoleConverter> _logger;
    private readonly IWebHostEnvironment _hostingEnvironment;
    
    public string ProcessPath { get; }
    public int EngineType { get; } = 2;
    public ImageConsoleConverter(ILogger<ImageConsoleConverter> logger, IWebHostEnvironment hostingEnvironment)
    {
        _logger = logger;
        _hostingEnvironment = hostingEnvironment;
        ProcessPath = _hostingEnvironment.WebRootPath + @$"\Tool\wkhtmltoimage.exe";
    }
    public bool ConvertContent(string inputPath, string outputPath)
    {
        try
        {
            var ticks = DateTime.UtcNow.Ticks;
            string processPdfpath = ProcessPath;

            Process process = new Process();
            process.StartInfo.UseShellExecute = true;
            process.StartInfo.FileName = processPdfpath;
            process.StartInfo.Arguments = $"\"{inputPath}\" \"{outputPath}\" ";
            process.Start();
        }
        catch (Exception ex)
        {
            _logger.LogCritical(ex.Message);
            return true;
        }       
        return true;
    }
}
  • Using the Engine in Our Methods. 
    public class BussinessConstants
{
    public static int ConvertEngineType_PDF = 1;
    public static int ConvertEngineType_Image = 2;
}

[ApiController]
[Route("[controller]")]
public class FileConvertController : ControllerBase
{
    private readonly ILogger<FileConvertController> _logger;
    private readonly IWebHostEnvironment _hostingEnvironment;
    private readonly IEnumerable<IConverterWebKitEngine> _converterWKs;

    public FileConvertController(
        ILogger<FileConvertController> logger,
        IWebHostEnvironment hostingEnvironment,
        IServiceProvider serviceScope)
    {
        _logger = logger;
        _hostingEnvironment = hostingEnvironment;
        _converterWKs = serviceScope.GetServices<IConverterWebKitEngine>();
    }

    [HttpGet("GetPDF")]
    public IEnumerable<string> GetPDF()
    {
        var ticks = DateTime.UtcNow.Ticks;

        var outputPdf = _hostingEnvironment.WebRootPath + $"\\OutputFiles\\Sync{ticks}.pdf";
        string inputPath = _hostingEnvironment.WebRootPath + $"\\InputFiles\\Sync{ticks}.html";
        
        string inputText = 
            "<html><head><title>Example of Paragraph tag</title></head><body style=\"line-height:1.6\">" +
            "<p><b>HTML</b> stands for <i><u>Hyper Text Markup Language.</u></i> It is used to create " +
            "web pages and applications. This language is easily understandable by the user and also " +
            "modifiable. It is actually a Markup language, hence it provides a flexible way for designing " +
            "the web pages along with the text.</p>HTML file is made up of different elements.<b>An element</b> " +
            "is a collection of <i>start tag, end tag, attributes and the text between them</i>.<p></p>" +
            "<h6>HTML to PDF / Image</h6><h5>HTML to PDF / Image</h5><h4>HTML to PDF / Image</h4>" +
            "<h3>HTML to PDF / Image</h3><h2>HTML to PDF / Image</h2><h1>HTML to PDF / Image</h1></body></html>";
        
        System.IO.File.WriteAllText(inputPath, inputText);

        if (_converterWKs.Any())
        {
            IConverterWebKitEngine converterWK = _converterWKs.FirstOrDefault(x => x.EngineType == BussinessConstants.ConvertEngineType_PDF);
            converterWK?.ConvertContent(inputPath, outputPdf);
        }

        return new List<string> { "A", "B" };
    }

    [HttpGet("GetImage")]
    public IEnumerable<string> GetImage()
    {
        var ticks = DateTime.UtcNow.Ticks;

        var outputImage = _hostingEnvironment.WebRootPath + $"\\OutputFiles\\Sync{ticks}.png";
        string inputPath = _hostingEnvironment.WebRootPath + $"\\InputFiles\\Sync{ticks}.html";

        string inputText = 
            "<html><head><title>Example of Paragraph tag</title></head><body style=\"line-height:1.6\">" +
            "<p><b>HTML</b> stands for <i><u>Hyper Text Markup Language.</u></i> It is used to create " +
            "web pages and applications. This language is easily understandable by the user and also " +
            "modifiable. It is actually a Markup language, hence it provides a flexible way for designing " +
            "the web pages along with the text.</p>HTML file is made up of different elements.<b>An element</b> " +
            "is a collection of <i>start tag, end tag, attributes and the text between them</i>.<p></p>" +
            "<h6>HTML to PDF / Image</h6><h5>HTML to PDF / Image</h5><h4>HTML to PDF / Image</h4>" +
            "<h3>HTML to PDF / Image</h3><h2>HTML to PDF / Image</h2><h1>HTML to PDF / Image</h1></body></html>";

        System.IO.File.WriteAllText(inputPath, inputText);

        if (_converterWKs.Any())
        {
            IConverterWebKitEngine converterWK = _converterWKs.FirstOrDefault(x => x.EngineType == BussinessConstants.ConvertEngineType_Image);
            converterWK?.ConvertContent(inputPath, outputImage);
        }

        return new List<string> { "A", "B" };
    }
}

Notes. (Please ensure the below points).

  • Ensure that the wkhtmltopdf.exe file is accessible by the C# application.
  • wkhtmltopdf works best with HTML files that are fully self-contained (e.g., inline CSS and JavaScript).
  • You may need to handle permissions if running on a server environment.

Conclusion

This method enables you to utilize wkhtmltopdf's rendering engine within C# applications, facilitating HTML-to-PDF and HTML-to-image conversions with high accuracy. With additional customization, you can modify this code to accommodate various document formats and needs.


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