PDFServicesSDK Execute command does not work when invoked from Windows Forms UI

Hi

I am new to using PDFServicesSDK - I have used example code from:

https://developer.adobe.com/document-services/docs/overview/pdf-services-api/quickstarts/dotnet/

To create a test example that will convert pdf to docx.

I wrapped the example in the following class:

    public class AdobeAPI
    {
        private const string PDF_SERVICES_CLIENT_ID = "clientid";
        private const string PDF_SERVICES_CLIENT_SECRET = "secret";

        public static void ExportToDocx()
        {
            try
            {
                var input = "d:\\Test.pdf";
                var output = "d:\\Test.docx";

                if (File.Exists(output))
                {
                    File.Delete(output);
                }

                // Initial setup, create credentials instance.                
                Credentials credentials = Credentials.ServicePrincipalCredentialsBuilder()
                    .WithClientId(PDF_SERVICES_CLIENT_ID)
                    .WithClientSecret(PDF_SERVICES_CLIENT_SECRET)
                    .Build();
                
                // Create an ExecutionContext using credentials and create a new operation instance.
                ExecutionContext executionContext = ExecutionContext.Create(credentials);
                ExportPDFOperation exportPdfOperation = ExportPDFOperation.CreateNew(ExportPDFTargetFormat.DOCX);
                // Provide an input FileRef for the operation.
                FileRef sourceFileRef = FileRef.CreateFromLocalFile(input);
                exportPdfOperation.SetInput(sourceFileRef);
                // Execute the operation.
                FileRef result = exportPdfOperation.Execute(executionContext);

                // Save the result to the specified location.
                result.SaveAs(output);
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }
    }

When I invoke this from Console Application:

namespace AdobeAPIConsole
{
    internal class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Start");
            AdobeAPI.ExportToDocx();
            Console.WriteLine("Done");
        }
    }
}

It works fine and file is being converted.

When I create a simple Windows Forms App with a single button and invoke this on button click:

namespace AdobeAPIWindowsForms
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void sbTest_Click(object sender, EventArgs e)
        { 
            AdobeAPI.ExportToDocx();
        }
    }
}

Then execution stops at:

// Execute the operation.
FileRef result = exportPdfOperation.Execute(executionContext);

 It doesn't crash, it doesn't throw any error. It simply hangs there forever.

What am I doing wrong, I need to be able to use PDFServicesSDK from Windows Forms app. Can anyone point me what can be the possible cause of this behaviour?

Thanks