# Preparing Documents for Electronic Signatures using MailMerge in C# > There are many benefits to using MS Word compatible templates to prepare documents for electronic signature capture. This article shows how to use MailMerge to prepare documents for the signing process. - **Author:** Bjoern Meyer - **Published:** 2023-07-05 - **Modified:** 2026-04-06 - **Description:** There are many benefits to using MS Word compatible templates to prepare documents for electronic signature capture. This article shows how to use MailMerge to prepare documents for the signing process. - **3 min read** (563 words) - **Tags:** - ASP.NET - ASP.NET Core - Electronic Signatures - PDF - **Web URL:** https://www.textcontrol.com/blog/2023/07/05/preparing-documents-for-electronic-signatures-using-mailmerge-in-csharp/ - **LLMs URL:** https://www.textcontrol.com/blog/2023/07/05/preparing-documents-for-electronic-signatures-using-mailmerge-in-csharp/llms.txt - **LLMs-Full URL:** https://www.textcontrol.com/blog/2023/07/05/preparing-documents-for-electronic-signatures-using-mailmerge-in-csharp/llms-full.txt --- Companies and organizations in every industry are recognizing the value of integrating electronic signatures into their workflows. Many e-signature services start the signature process with a pre-generated PDF document that comes from applications such as MS Word or ERP systems. ### Dynamic Templates However, a document should be able to be edited for as long as possible. It is a dynamic structure that should be able to be updated at any time until the process is complete and a document is created for further processing or archiving. ### MS Word Compatible Instead of a sealed PDF document, the document signing process starts with an MS Word compatible template. This gives developers the flexibility they need to integrate the entire pipeline of digital document processing into their own workflows. Typically, the signature process starts with a template consisting of merge field placeholders and form fields that are pre-populated before the generated document is passed to the signature workflow. A simple template consisting of a standard layout, static data, dynamic merge, and form fields is shown in the following screenshot: ![Creating documents with TX Text Control](https://s1-www.textcontrol.com/assets/dist/blog/2023/07/05/a/assets/template.webp "Creating documents with TX Text Control") ### Pre-Populate Fields Before you use the Document Viewer to deliver this document to the end user, you can prepare it by merging the data you know into the document. The following code uses the MailMerge class to merge a data object into the template. ``` byte[] document; using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl()) { tx.Create(); tx.Load("App_Data/vaccination_form.tx", TXTextControl.StreamType.InternalUnicodeFormat); using (TXTextControl.DocumentServer.MailMerge mm = new TXTextControl.DocumentServer.MailMerge()) { mm.TextComponent = tx; mm.FormFieldMergeType = TXTextControl.DocumentServer.FormFieldMergeType.Preselect; mm.RemoveEmptyFields = false; // pre-select form fields with known data and merge // data into merge fields mm.MergeObject(data); } tx.Save(out document, TXTextControl.BinaryStreamType.InternalUnicodeFormat); } ``` ### Capturing Signatures The pre-populated document is then loaded into the Document Viewer to capture user data and the final signature. ![Creating documents with TX Text Control](https://s1-www.textcontrol.com/assets/dist/blog/2023/07/05/a/assets/viewer2.webp "Creating documents with TX Text Control") ### Digital Signing When the document is submitted, the Document Viewer automatically merges the completed form field values and captured signature into the document. Finally, server-side certificate signing is performed to retrieve a fully digitally signed and tamper-proofed PDF document. ``` [HttpPost] public string ExportPDF() { Stream inputStream = Request.InputStream; inputStream.Position = 0; StreamReader str = new StreamReader(inputStream); string sBuf = str.ReadToEndAsync().Result; TXTextControl.Web.MVC.DocumentViewer.Models.SignatureData data = JsonConvert.DeserializeObject(sBuf); byte[] bPDF; // create temporary ServerTextControl using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl()) { tx.Create(); // load the document tx.Load(Convert.FromBase64String(data.SignedDocument.Document), TXTextControl.BinaryStreamType.InternalUnicodeFormat); FlattenFormFields(tx); X509Certificate2 cert = new X509Certificate2(Server.MapPath("~/App_Data/textcontrolself.pfx"), "123"); TXTextControl.SaveSettings saveSettings = new TXTextControl.SaveSettings() { CreatorApplication = "TX Text Control Sample Application", //DigitalSignature = new TXTextControl.DigitalSignature(cert, null), SignatureFields = new DigitalSignature[] { new TXTextControl.DigitalSignature(cert, null, "txsign"), new TXTextControl.DigitalSignature(cert, null, "txsign_init")} }; // save the document as PDF tx.Save(out bPDF, TXTextControl.BinaryStreamType.AdobePDFA, saveSettings); } // return as Base64 encoded string return Convert.ToBase64String(bPDF); } ``` When you open the generated document, you can see the validity of the signature fields in the Acrobat Reader. ![Creating documents with TX Text Control](https://s1-www.textcontrol.com/assets/dist/blog/2023/07/05/a/assets/results.webp "Creating documents with TX Text Control") --- ## About Bjoern Meyer As CEO, Bjoern is the visionary behind our strategic direction and business development, bridging the gap between our customers and engineering teams. His deep passion for coding and web technologies drives the creation of innovative products. If you're at a tech conference, be sure to stop by our booth - you'll most likely meet Bjoern in person. With an advanced graduate degree (Dipl. Inf.) in Computer Science, specializing in AI, from the University of Bremen, Bjoern brings significant expertise to his role. In his spare time, Bjoern enjoys running, paragliding, mountain biking, and playing the piano. - [LinkedIn](https://www.linkedin.com/in/bjoernmeyer/) - [X](https://x.com/txbjoern) - [GitHub](https://github.com/bjoerntx) --- ## Related Posts - [Replace Words at the Input Position with Formatted Content from a Web API](https://www.textcontrol.com/blog/2023/07/06/replace-words-at-the-input-position-with-formatted-content-from-a-web-api/llms.txt) - [Why Structured E-Invoices Still Need Tamper Protection using C# and .NET](https://www.textcontrol.com/blog/2026/03/24/why-structured-e-invoices-still-need-tamper-protection-using-csharp-and-dotnet/llms.txt) - [Create Fillable PDFs from HTML Forms in C# ASP.NET Core Using a WYSIWYG Template](https://www.textcontrol.com/blog/2026/03/17/create-fillable-pdfs-from-html-forms-in-csharp-aspnet-core-using-a-wysiwyg-template/llms.txt) - [Why HTML to PDF Conversion is Often the Wrong Choice for Business Documents in C# .NET](https://www.textcontrol.com/blog/2026/03/13/why-html-to-pdf-conversion-is-often-the-wrong-choice-for-business-documents-in-csharp-dot-net/llms.txt) - 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