test.cs

public IActionResult CreatePDF()
{
    // new non-UI ServerTextControl
    using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl()) {

        tx.Create();

        // create a selection object
        TXTextControl.Selection selection = new TXTextControl.Selection() {
            FontSize = 1000,
            Text = "Welcome to Text Control",
            Bold = true,
            ForeColor = System.Drawing.Color.DarkRed
        };

        // apply the selection
        tx.Selection = selection;

        // save the document into a byte array
        byte[] document;
        tx.Save(out document, TXTextControl.BinaryStreamType.AdobePDF);

        // create and return a file
        MemoryStream stream = new MemoryStream(document);
        stream.Position = 0;

        FileStreamResult fileStreamResult = new FileStreamResult(stream, "application/pdf");

        fileStreamResult.FileDownloadName = "results.pdf";
        return fileStreamResult;
    }
}