IncludeText fields can be used to merge external references into a mail merge template using the reporting engine TXTextControl.DocumentServer.MailMerge class. External documents of type DOC, DOCX, RTF and TX can be referenced and are automatically included during the merge process.

The TXTextControl.DocumentServer.MailMerge.IncludeTextMerging event can be used to inject other files or formatted text by returning a document in the event. The following code shows how to handle Excel file references:

private void MailMerge_IncludeTextMerging(object sender,
    TXTextControl.DocumentServer.MailMerge.IncludeTextMergingEventArgs e)
{
    // custom handing of XLSX files
    switch (Path.GetExtension(e.IncludeTextField.Filename))
    {
        case ".xlsx": // Excel file detected

            if (!File.Exists(e.IncludeTextField.Filename))
                return;

            // load document into temp. ServerTextControl
            using (TXTextControl.ServerTextControl tx =
                new TXTextControl.ServerTextControl())
            {
                tx.Create();

                // Bookmark name is the sheet name of the Excel document
                TXTextControl.LoadSettings ls = new TXTextControl.LoadSettings()
                {
                    DocumentPartName = e.IncludeTextField.Bookmark
                };

                try
                {
                    // load the Excel document
                    tx.Load(
                        e.IncludeTextField.Filename, 
                        TXTextControl.StreamType.SpreadsheetML, 
                        ls);
                }
                catch {
                    return;
                }

                byte[] data;

                // save the document using the TX format
                tx.Save(out data, 
                    TXTextControl.BinaryStreamType.InternalUnicodeFormat);

                e.IncludeTextDocument = data; // pass back to the field
            }

            break;
    }
}

In case the reference ends with .xlsx, the file is loaded into a temporary TXTextControl.ServerTextControl class. The Bookmark property of the IncludeTextField is used to define the sheet name in the Excel document. After the document is loaded successfully into ServerTextControl, it is exported in the internal TX Text Control format and returned to the TXTextControl.DocumentServer.MailMerge.IncludeTextMergingEventArgs.IncludeTextDocument property.

The following screen video shows this in action:

Download this sample from our GitHub repository and try this on your own.