The MailMerge class can be used to merge form fields with data from JSON objects or IEnumerable objects. Form fields can be pre-populated to prepare forms for users to complete or they can be flattened.

We just published a new online demo that shows how to implement these options based on a typical form used in the healthcare industry.

Pre-Selecting Form Fields

On the first button click, the form fields are pre-selected with existing JSON data. To increase the user experience, to accelerate the process and to decrease errors, parts of a document can be pre-populated with known values.

The HttpGet controller method PDFPrepare is called with the boolean flatten parameter false.

[HttpGet]
public string PDFPrepare(bool flatten) {
   byte[] bDocument;

   // create temporary ServerTextControl
   using (ServerTextControl tx = new ServerTextControl()) {
      tx.Create();

      // loading the template
      tx.Load(Server.MapPath("~/App_Data/Documents/patient_history.tx"), StreamType.InternalUnicodeFormat);

      // fire up the MailMerge engine
      using (MailMerge mailMerge = new MailMerge()) {
         mailMerge.TextComponent = tx; // connect to ServerTextControl

         // pre-selecting form fields         
         if (flatten == false)
            mailMerge.FormFieldMergeType = FormFieldMergeType.Preselect;
         else // flatten form fields
            mailMerge.FormFieldMergeType = FormFieldMergeType.Replace;

         string jsonData = System.IO.File.ReadAllText(Server.MapPath("~/App_Data/Documents/data.json"));
         
         // merge JSON into fields
         mailMerge.MergeJsonData(jsonData);
      }

      // export to PDF
      tx.Save(out bDocument, BinaryStreamType.InternalUnicodeFormat);
   }

   // return as Base64 encoded string
   return Convert.ToBase64String(bDocument);
}

In this case, the FormFieldMergeType property is set to Preselect which basically tells the MailMerge engine to set the text of the form fields and to keep the form fields in the document.

Flattening Form Fields

On the second button, the controller method PDFPrepare is called with the boolean flatten parameter true. The FormFieldMergeType property is set to Replace. In this case, the MailMerge engine is removing known form fields and replaces them with the given text.

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