This App scripts code take a list of details in a google sheet and replaces the details in a Google doc.

Google App Scripts Document template generator

function onOpen() {
  var menuEntries = [ {name: "Create Autofilled Template", functionName: "AutofillDocFromTemplate"}];
  var ss = SpreadsheetApp.getActiveSpreadsheet();;
  ss.addMenu("My Menu", menuEntries);
}

function AutofillDocFromTemplate(){
  var templateid = "GOOGLE-DOCS-TEMPLATE-ID-GOES-HERE"; // this is the template file id. You can find this in the URL of the google document template. For example, if your URL Looks like this: https://docs.google.com/document/d/1SDTSW2JCItWMGkA8cDZGwZdAQa13sSpiYhiH-Kla6VA/edit, THEN the ID would be 1SDTSW2JCItWMKkA8cDZGwZdAQa13sSpiYhiH-Kla6VA
  var FOLDER_NAME = "GOOGLE-DRIVE-FOLDER-NAME"; // Enter the name of the folder where you want to save your new documents. for example, this could be "Output Folder".
  
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getActiveSheet();
  var data = sheet.getRange(2, 1, sheet.getLastRow()-1, sheet.getLastColumn()).getValues(); 
 
  var usernamefordoctitle = "Oceanspring" //sheet.getRange(2, 1, 1, 1).getValues(); 
  var newDoc = DocumentApp.create("Template for " +usernamefordoctitle);
  var file = DriveApp.getFileById(newDoc.getId());
  var folder = DriveApp.getFolderById("FOLDER-KEY-GOES-HERE"); // INSERT the destination folder ID. Once again, this can be found in the URL once you have the folder openned in your browser
  folder.addFile(file)

  for (var i in data){
    var row = data[i];
    Logger.log(row)
    
    var docid = DriveApp.getFileById(templateid).makeCopy().getId();
    var doc = DocumentApp.openById(docid);
    
    var body = doc.getActiveSection();
    
    if(row[0].length<=0 || row[2].length>10 || row[3].length<11){}
    else{
      body.replaceText("%NAME%", row[0]);
      body.replaceText("%TELEPHONE%", row[2]);
      body.replaceText("%LOYALTYID%", row[3]); // To add more auto gen fields, add them below along with the column number
      //body.replaceText("%ENDTEMPLATE%", "\n")
      body.appendPageBreak(); //Add Page break
      
      appendToDoc(doc, newDoc)
      //appendElementToDoc(doc, newDoc)
    }
    
    
    
  }
  
  doc.saveAndClose()
  newDoc.saveAndClose()
  
  
    var message = "Attached is an auto generated template for loyalty customers!"; // Customize message
    var emailTo = "[email protected]" // replace with your email
    var subject = "Loyalty Customers auto generated template"; // customize subject 
    var pdf = DriveApp.getFileById(newDoc.getId()).getAs('application/pdf').getBytes();
    var attach = {fileName:'Autogenerated template.pdf',content:pdf, mimeType:'application/pdf'}; // customize file name: "Autogenerated template"
    MailApp.sendEmail(emailTo, subject, message, {attachments:[attach]});
    
    //DriveApp.getFileById(docid).setTrashed(true);
    
  ss.toast("Template has been complied and emailed to you as PDF. Please check your mail");
}

function appendToDoc(src, dst) {
  var srcBody = src.getActiveSection().getParagraphs();
  var dstBody = dst.getActiveSection();
  var srcBodyLength = srcBody.length
  
  for(i=0; i<srcBody.length; i++){
    if (i==srcBodyLength-1){
      dstBody.appendPageBreak()
    }
    else{
      var p = srcBody[i].removeFromParent()
      dstBody.appendParagraph(p)
    }
  }
  Logger.log("appended oo")
  
}


function appendElementToDoc(srcDoc, destDoc) {
  var docChildren = srcDoc.getNumChildren();
  
  for(i=0; i<srcDoc.getNumChildren()-1; i++){
    var child = srcDoc.getChild(i).removeFromParent()
    var type = child.getType();
    Logger.log("Element "+i+" type is "+type);
    
    if (type == "PARAGRAPH") {
      destDoc.getActiveSection().appendParagraph(child);
    } 
    else{
      destDoc.appendPageBreak()
    }
  }

}