HtmlToPdfConverter.cs

using System;
using System.Diagnostics;
using System.IO;

public interface IHtmlToPdfConverter
{
    byte[] Convert(string basePath, string htmlCode, FormatType formatType, OrientationType orientationType);
}

public class HtmlToPdfConverter : IHtmlToPdfConverter
{
    public byte[] Convert(string basePath, string htmlCode, FormatType formatType = FormatType.A4, OrientationType orientationType = OrientationType.Portrait)
    {
        var inputFileName = $"input_{Guid.NewGuid()}.html";
        var outputFileName = $"output_{Guid.NewGuid()}.pdf";
        File.WriteAllText($"{basePath}/{inputFileName}", htmlCode);
        var startInfo = new ProcessStartInfo("phantomjs.exe")
                            {
                                WorkingDirectory = basePath,
                                Arguments = $"rasterize.js \"{inputFileName}\" \"{outputFileName}\" \"{formatType}\" \"{orientationType.ToString().ToLower()}\"",
                                UseShellExecute = true,
                            };

        var process = new Process { StartInfo = startInfo };
        process.Start();

        process.WaitForExit();

        var bytes = File.ReadAllBytes($"{basePath}/{outputFileName}");

        File.Delete($"{basePath}/{inputFileName}");
        File.Delete($"{basePath}/{outputFileName}");

        return bytes;
    }
}