How to use OnExecutionContextCreated method of PuppeteerSharp.Worker class

You could use a using block for that:

public static async Task<string> renderHtmlAsync(string url2)
{
    await new BrowserFetcher().DownloadAsync(BrowserFetcher.DefaultChromiumRevision);
    using (Browser browser = await Puppeteer.LaunchAsync(new LaunchOptions
    {
        Headless = true
    }))
    {
        var page = await browser.NewPageAsync();
        page.DefaultTimeout = 0;
        var navigation = new NavigationOptions
        {
            Timeout = 0,
            WaitUntil = new[] {
                    WaitUntilNavigation.DOMContentLoaded }
        };
        await page.GoToAsync(url2, navigation);
        var content = page.GetContentAsync();

        return await content;
    }
}

This works like:

var myObject = new DispoableObject();
try
{
    // insert code
    return result;
}
finally
{
    myObject.Dispose();
}

The code in the finally is always executed, even when an exception is thrown inside the try block.

First, the evaluate function won't get what you write in the console.log. You need to return something. As you are waiting for an event you can return a promise and resolve that promise inside the event.

page.EvaluateFunctionAsync<Point>(@"() => {
  return new Promise(resolve => {
    document.onmousemove = function(e){
      mouseX = e.offsetX;
      mouseY = e.offsetY;
      resolve({x: mouseX, y: mouseY});
    };
  });
}");

Try this:

public static async Task<string> ExportPdfASync(string url, string location)
{
 try
 {
   using (var browser = await Puppeteer.LaunchAsync(LaunchOptions))
   using (var page = await browser.NewPageAsync())
   {
    await page.SetViewportAsync(new ViewPortOptions() { Width = 1440, Height = 990, IsMobile = false, DeviceScaleFactor = 1.0 });

    await page.SetJavaScriptEnabledAsync(true);
    await page.GoToAsync(url);
    await page.WaitForTimeoutAsync(1500);

    var marginOptions = new MarginOptions()
    {
        Top = "10mm",
        Left = "10mm",
        Right = "10mm",
        Bottom = "10mm"
    };

    var pdfOptions = new PdfOptions()
    {
        PrintBackground = true,
        Format = PaperFormat.A4,
        MarginOptions = marginOptions,
        Landscape = landscape
    };
    await page.PdfAsync(location, pdfOptions);
  }
  }
  catch (Exception ex)
  {
  }
  finally {
    browser.CloseAsync();
    page.CloseAsync();
  }
  return "";
}

The problem is how the CSSStyleDeclaration is serialized. If that´s how Chromium decides to serialize that object there is nothing we can do there.

But, we can try to solve that from javascript using EvaluateFunctionAsync.

foreach (var handle in elementHandles)
{
  var style = await page.EvaluateFunctionAsync<Dictionary<string, string>>(
    "e => Object.entries(e.style).filter(i => isNaN(i[0]) && i[1]).map(i => { return { [i[0]] : i[1]}}).reduce((acc, cur) => { return {...acc, ...cur}}, {})", handle);
  var output = style.ToString();
}

Let's take a look at the javascript expression

e=> //We send the HTML element instead of the style property
  Object.entries(e.style) //We get all the property/value pairs from the CSSStyleDeclaration object
    // We want to exclude number properties (like 0,1,2) and empty values
    .filter(i => isNaN(i[0]) && i[1]) 
    //We turn them into objects
    .map(i => { return { [i[0]] : i[1]}})
    //We merge them into one single object that will be returned to C#
    .reduce((acc, cur) => { return {...acc, ...cur}}, {})

I think you should not do a .ConfigureAwait on the controller level, look at this article for more information: https://blog.stephencleary.com/2017/03/aspnetcore-synchronization-context.html.

ASP.NET team dropped the use of SynchronizationContext, so using it in your controller is pointless.

As the article states, you should still use it on your service level, as you don't know whether or not a UI could plug itself to the service and use it, but on your WEB API, you can drop it.

How to use PuppeteerSharp inside an UWP App?

PuppeteerSharp does not support in UWP, You could check PuppeteerSharp source code to verify this. This is DownloadsFolder = Path.Combine(Directory.GetCurrentDirectory(), ".local-chromium") and matched path is "{AppRoot}\bin\x86\Debug\AppX.local-chromium". In the following code we call Create method in it, but above path is read-only in UWP.

    public async Task<RevisionInfo> DownloadAsync(int revision)
    {
        var url = GetDownloadURL(Platform, DownloadHost, revision);
        var zipPath = Path.Combine(DownloadsFolder, $"download-{Platform.ToString()}-{revision}.zip");
        var folderPath = GetFolderPath(revision);

        if (new DirectoryInfo(folderPath).Exists)
        {
            return RevisionInfo(revision);
        }

        var downloadFolder = new DirectoryInfo(DownloadsFolder);
        if (!downloadFolder.Exists)
        {
            downloadFolder.Create();
        }

        if (DownloadProgressChanged != null)
        {
            _webClient.DownloadProgressChanged += DownloadProgressChanged;
        }
        await _webClient.DownloadFileTaskAsync(new Uri(url), zipPath).ConfigureAwait(false);

        if (Platform == Platform.MacOS)
        {
            //ZipFile and many others unzip libraries have issues extracting .app files
            //Until we have a clear solution we'll call the native unzip tool
            //https://github.com/dotnet/corefx/issues/15516
            NativeExtractToDirectory(zipPath, folderPath);
        }
        else
        {
            ZipFile.ExtractToDirectory(zipPath, folderPath);
        }

        new FileInfo(zipPath).Delete();

        var revisionInfo = RevisionInfo(revision);

        if (revisionInfo != null && GetCurrentPlatform() == Platform.Linux)
        {
            LinuxSysCall.Chmod(revisionInfo.ExecutablePath, LinuxSysCall.ExecutableFilePermissions);
        }
        return revisionInfo;
    }

Based on Line 43 of the LanchOptions.cs you can specify arguments to the launch process.

Now connecting this with the native JavaScript (using the --load-extension flag) the output should look similar to the following:

var browser = await Puppeteer.LaunchAsync(new LaunchOptions
{
    Args = new string[1] { "--load-extension=/Path/To/Extension/Folder" }
});

Note: that I put path to folder, not the .zip as you have in your sample.. if you want to load multiple extensions then just separate the paths using a comma.

Here's a full list of possible arguments that can be passed in to Chromium.

Try to disable some of the security features that can be disabled when launching puppeteer.

Check in puppeteer chrome://flags/ in case there's something blocking iframe access, maybe is insecure content or maybe you have to be explicit about isolation trial.

My 2 cents on this, it should allow it to access it from non secure

Args = new[]
    {
        "--disable-web-security",
        "--disable-features=IsolateOrigins,site-per-process,BlockInsecurePrivateNetworkRequests",
        "--disable-site-isolation-trials"
    }

using below,

using var page = browser.NewPageAsync().Result;

page.TypeAsync("input[name='elementname']", valuetobeset).Wait();