test.cs

public class DocumentController : Controller
{
  [HttpPost]
  public IActionResult Merge(
    [FromBody] MergeBody mergeBody)
  {

    #region Error Checking

    // error checking: MergeBody cannot be null
    if (mergeBody == null)
    {
      return BadRequest();
    }

    // error checking: Template must not be null
    if (mergeBody.Template == null)
    {
      return BadRequest("Template must not be null");
    }

    #endregion

    using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl())
    {
      tx.Create();

      // load the template
      try {         
        tx.Load(Convert.FromBase64String(mergeBody.Template), TXTextControl.BinaryStreamType.InternalUnicodeFormat);
      }
      catch (Exception ex) // format not valid
      {
        return BadRequest(ex.Message);
      }

      // create a new MailMerge object
      MailMerge mailMerge = new MailMerge()
      {
        TextComponent = tx,
        
        // set the merge settings
        DataSourceCulture = new CultureInfo(mergeBody.MergeSettings.DataSourceCulture),
        FormFieldMergeType = (FormFieldMergeType)mergeBody.MergeSettings.FormFieldMergeType,
        MergeCulture = new CultureInfo(mergeBody.MergeSettings.MergeCulture),
        RemoveEmptyBlocks = mergeBody.MergeSettings.RemoveEmptyBlocks ?? false,
        RemoveEmptyFields = mergeBody.MergeSettings.RemoveEmptyFields ?? false,
        RemoveEmptyImages = mergeBody.MergeSettings.RemoveEmptyImages ?? false,
        RemoveEmptyLines = mergeBody.MergeSettings.RemoveEmptyLines ?? false,
        RemoveTrailingWhitespace = mergeBody.MergeSettings.RemoveTrailingWhitespace ?? false,
      };

      // merge the data
      mailMerge.MergeJsonData(mergeBody.MergeData, true);

      // save settings
      TXTextControl.SaveSettings saveSettings = new TXTextControl.SaveSettings()
      {
        Author = mergeBody.MergeSettings.Author,
        CreationDate = (DateTime)mergeBody.MergeSettings.CreationDate,
        CreatorApplication = mergeBody.MergeSettings.CreatorApplication,
        DocumentSubject = mergeBody.MergeSettings.DocumentSubject,
        DocumentTitle = mergeBody.MergeSettings.DocumentTitle,
        LastModificationDate = (DateTime)mergeBody.MergeSettings.LastModificationDate,
        UserPassword = mergeBody.MergeSettings.UserPassword
      };

      byte[] results = null;

      // save the document as PDF
      tx.Save(out results, TXTextControl.BinaryStreamType.AdobePDF, saveSettings);

      // return the merged document as base64 string
      return Ok(Convert.ToBase64String(results));
    }
  }
}