C# – Convert HTML to PDF using Pechkin (WkHtmlToPdf)

There are a lot of C# libraries that can be used to create PDF files but I needed one that was able to convert an HTML file (with CSS and images) into a PDF document. Searching for a solution I found good reviews for a free library called Pechkin so I decided to give it a try.

While using it I stumbled upon some little problems but in the end I was satisfied with the result hence this post where I will detail my experience with this library.

Pechkin is a .NET Wrapper for another library called WkHtmlToPdf that uses the WebKit engine to convert HTML pages to PDF… and this is a pretty good reason to give it a try. If not yet convinced, below is a description of WebKit taken from Wikipedia:

WebKit is a layout engine software component designed to allow web browsers to render web pages. It powers Google’s Chrome web browser versions up to 27, and Apple’s Safari web browser applications. As of November 2012 it has the most market share of any layout engine at over 40% of the browser market share — ahead of both the Trident engine used by Internet Explorer, and the Gecko engine used by Firefox.

It is also used as the basis for the experimental browser included with the Amazon Kindle e-book reader, as well as the default browser in the Apple iOS, Android, BlackBerry 10, and Tizen mobile operating systems.

For testing the library I created a simple web application that reads the HTML content at a given URL and generates a PDF file. You can download it from Codeplex: https://pechkinwebtest.codeplex.com/. After trying with different URLs I got:

• very good results for the sites with a simple, clean CSS like http://www.adobe.com/products/acrobat.html (see the generated PDF here),
• good results for bigger pages like http://www.weather.com (see the generated PDF here) – but it needed some seconds to generate the file,
• poor results for the pages with complex CSS like http://www.adobe.com (see the generated PDF here),
• and excellent results for my simple pages, created specially for being converted to PDF :).

Problems and Solutions:

1. Gif images are not supported – I couldn’t find any solution for this one.
2. With the original Pechkin library the DLLs used for rendering the PDF remain hanging in memory:
   • If used inside a web application, the libraries that generate the PDF remain loaded in the memory indefinitely after making a new deploy. For example, if you run the site using the Visual Studio built-in web server and then you generate a PDF file the libraries will get loaded into memory. If, after that, you rebuild and run the site using the same built-in server you will get some errors like the one below.
     

     Could not copy “C:\WebSite\libgcc_s_dw2-1.dll” to “bin\libgcc_s_dw2-1.dll”. Exceeded retry count of 10.

     So I had to stop and restart the the server. You’ll get the same behavior when deploying to IIS. More details about this issue here: https://github.com/gmanny/Pechkin/issues/12

   • Solution: Someone made a branch of the original project and solved this issue, so make sure to use this project https://github.com/tuespetre/Pechkin and not the original one that is here: https://github.com/gmanny/Pechkin
3. Images under HTTPS are not rendered inside the PDF. Solution: Download and install OpenSSL on the server (More details here: http://www.openssl.org/related/binaries.html)

How to use it:

1. Download and compile this branch of the Pechkin project: https://github.com/tuespetre/Pechkin (This will solve the DLL hanging problem :)). Or, if you’re lazy, you can download here the needed DLLs.
2. Inside your web application solution add a reference to: Common.Logging.dll and Pechkin.dll.
   
3. Add to the root of your solution the following DLLs and set from the properties window: Copy to output directory » Copy always.
4. Now you can start generating PDF files from HTML strings. Below is a very simple example that does this:

   //Transform the HTML into PDF
   var pechkin = Factory.Create(new GlobalConfig());
   var pdf = pechkin.Convert(new ObjectConfig()
   						.SetLoadImages(true).SetZoomFactor(1.5)
   						.SetPrintBackground(true)
   						.SetScreenMediaType(true)
   						.SetCreateExternalLinks(true), html);
   
   //Return the PDF file
   Response.Clear();
   
   Response.ClearContent();
   Response.ClearHeaders();
   
   Response.ContentType = "application/pdf";
   Response.AddHeader("Content-Disposition", string.Format("attachment;filename=test.pdf; size={0}", pdf.Length));
   Response.BinaryWrite(pdf);
   
   Response.Flush();
   Response.End();
   

5. After publishing it to IIS, select the application pool for your web site, then right-click and select Advanced Settings... Here make sure to enable 32-bit applications otherwise you will get this error:
   

   Could not load file or assembly ‘Pechkin’ or one of its dependencies. An attempt was made to load a program with an incorrect format.

   

The source code of the test application, together with the Pechkin DLLs and the OpenSSL installer (Win32OpenSSL_Light-1_0_1e.exe) can be downloaded from Codeplex.