EDIT (2024) : new method related to webview and Edge https://weblog.west-wind.com/posts/2024/Mar/26/Html-to-PDF-Generation-using-the-WebView2-Control

This will need Windows OS.

I have tested with ASP.net Core application and I used .net8.0-windows as target framework in order to use this nuget I also installed webview runtime

Also creator indicated windows desktop runtime as dependency too.

Install the nuget.

/// <summary>
/// Return raw data as PDF
/// </summary>
/// <returns></returns>
[HttpGet("rawpdfex")]
public async Task<IActionResult> RawPdf()
{
    var file = Path.GetFullPath("./HtmlSampleFile-SelfContained.html");

    var pdf = new HtmlToPdfHost();
    var pdfResult = await pdf.PrintToPdfStreamAsync(file, new 
        WebViewPrintSettings { PageRanges = "1-10" });

    if (pdfResult == null || !pdfResult.IsSuccess)
    {
        Response.StatusCode = 500;                
        return new JsonResult(new
        {
            isError = true,
            message = pdfResult.Message
        });
    }

    return new FileStreamResult(pdfResult.ResultStream, "application/pdf");             
}

EDIT: New Suggestion HTML Renderer for PDF using PdfSharp

(After trying wkhtmltopdf and suggesting to avoid it)

HtmlRenderer.PdfSharp is a 100% fully C# managed code, easy to use, thread safe and most importantly FREE (New BSD License) solution.

Usage

1. Download HtmlRenderer.PdfSharp nuget package.

2. Use Example Method.

   public static Byte[] PdfSharpConvert(String html)
   {
       Byte[] res = null;
       using (MemoryStream ms = new MemoryStream())
       {
           var pdf = TheArtOfDev.HtmlRenderer.PdfSharp.PdfGenerator.GeneratePdf(html, PdfSharp.PageSize.A4);
           pdf.Save(ms);
           res = ms.ToArray();
       }
       return res;
   }
   

A very Good Alternate Is a Free Version of iTextSharp

Until version 4.1.6 iTextSharp was licensed under the LGPL licence and versions until 4.16 (or there may be also forks) are available as packages and can be freely used. Of course someone can use the continued 5+ paid version.

I tried to integrate wkhtmltopdf solutions on my project and had a bunch of hurdles.

I personally would avoid using wkhtmltopdf - based solutions on Hosted Enterprise applications for the following reasons.

1. First of all wkhtmltopdf is C++ implemented not C#, and you will experience various problems embedding it within your C# code, especially while switching between 32bit and 64bit builds of your project. Had to try several workarounds including conditional project building etc. etc. just to avoid "invalid format exceptions" on different machines.
2. If you manage your own virtual machine its ok. But if your project is running within a constrained environment like (Azure (Actually is impossible withing azure as mentioned by the TuesPenchin author) , Elastic Beanstalk etc) it's a nightmare to configure that environment only for wkhtmltopdf to work.
3. wkhtmltopdf is creating files within your server so you have to manage user permissions and grant "write" access to where wkhtmltopdf is running.
4. Wkhtmltopdf is running as a standalone application, so its not managed by your IIS application pool. So you have to either host it as a service on another machine or you will experience processing spikes and memory consumption within your production server.
5. It uses temp files to generate the pdf, and in cases Like AWS EC2 which has really slow disk i/o it is a big performance problem.
6. The most hated "Unable to load DLL 'wkhtmltox.dll'" error reported by many users.

--- PRE Edit Section ---

For anyone who want to generate pdf from html in simpler applications / environments I leave my old post as suggestion.

TuesPechkin

https://www.nuget.org/packages/TuesPechkin/

or Especially For MVC Web Applications (But I think you may use it in any .net application)

Rotativa

https://www.nuget.org/packages/Rotativa/

They both utilize the wkhtmtopdf binary for converting html to pdf. Which uses the webkit engine for rendering the pages so it can also parse css style sheets.

They provide easy to use seamless integration with C#.

Rotativa can also generate directly PDFs from any Razor View.

Additionally for real world web applications they also manage thread safety etc...

pandoc is a great command-line tool for file format conversion.

The disadvantage is for PDF output, you’ll need LaTeX. The usage is

pandoc test.html -t latex -o test.pdf

If you don't have LaTeX installed, then I recommend htmldoc.

Cited from Creating a PDF

By default, pandoc will use LaTeX to create the PDF, which requires that a LaTeX engine be installed.

Alternatively, pandoc can use ConTeXt, pdfroff, or any of the following HTML/CSS-to-PDF-engines, to create a PDF: wkhtmltopdf, weasyprint or prince. To do this, specify an output file with a .pdf extension, as before, but add the --pdf-engine option or -t context, -t html, or -t ms to the command line (-t html defaults to --pdf-engine=wkhtmltopdf).