test.cs

[ApiController]
[Route("api/[controller]")]
public class TextControlController : ControllerBase
{
  [HttpGet]
  [Route("LoadDocument")]
  public TextControlDocument LoadDocument(string DocumentName) {
     using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl()) {
        tx.Create();
        tx.Load("App_Data/" + DocumentName, TXTextControl.StreamType.WordprocessingML);

        byte[] data;

        tx.Save(out data, TXTextControl.BinaryStreamType.InternalUnicodeFormat);

        return new TextControlDocument() { Document = Convert.ToBase64String(data) };
     }
  }

}