private void btnExecute_Click(object sender, EventArgs e) { if (String.IsNullOrEmpty(txtXmlFileName.Text) || String.IsNullOrEmpty(txtXslFileName.Text)) { MessageBox.Show("You must choose XML and XSL(T) files before continue!", "Stop", MessageBoxButtons.OK, MessageBoxIcon.Stop); } else { try { using (var transformer = new XslTransformer()) { transformer.Initialize(txtXslFileName.Text); txtOutput.Text = transformer.GenerateString(openXml.OpenFile()); } } catch (Exception ex) { MessageBox.Show(ex.ToString(), "Error", MessageBoxButtons.OK, MessageBoxIcon.Error); } } }