test.cs

using Microsoft.AspNetCore.Mvc;
using System.Security.Cryptography.X509Certificates;
using TXTextControl;
using TXTextControl.Web.MVC.DocumentViewer;
using TXTextControl.Web.MVC.DocumentViewer.Models;

namespace MyAngularBackend.Server.Controllers
{
  [ApiController]
  [Route("[controller]")]
  public class DocumentController : ControllerBase
  {

    private readonly ILogger<DocumentController> _logger;

    public DocumentController(ILogger<DocumentController> logger)
    {
      _logger = logger;
    }

    [HttpGet]
    [Route("Load")]
    public DocumentData Load()
    {
      // open file as byte and convert to base64
      byte[] fileBytes = System.IO.File.ReadAllBytes("App_Data/document.tx");
      string file = Convert.ToBase64String(fileBytes);
      return new DocumentData { Name = "document.pdf", Document = file };
    }

    [HttpPost]
    [Route("Sign")]
    public string Sign([FromBody] SignatureData signatureData)
    {
      byte[] bPDF;

      // create temporary ServerTextControl
      using (ServerTextControl tx = new ServerTextControl())
      {
        tx.Create();

        // load the document
        tx.Load(Convert.FromBase64String(signatureData.SignedDocument.Document),
          BinaryStreamType.InternalUnicodeFormat);

        // create a certificate
        X509Certificate2 cert = new X509Certificate2("App_Data/textcontrol_self.pfx", "123");

        // create a list of digital signatures
        var signatureFields = new List<DigitalSignature>();

        // create a digital signature for each signature box
        foreach (SignatureBox box in signatureData.SignatureBoxes)
        {
          signatureFields.Add(new DigitalSignature(cert, null, box.Name));
        }

        // create save settings
        SaveSettings saveSettings = new SaveSettings()
        {
          CreatorApplication = "Your Application",
          SignatureFields = signatureFields.ToArray()
        };

        // save the document as PDF
        tx.Save(out bPDF, BinaryStreamType.AdobePDFA, saveSettings);
      }

      // return as Base64 encoded string
      return Convert.ToBase64String(bPDF);
    }
  }
}