another version in Google Script

ereserve-index-builder.js

function getAllFolders(){
  let doc = DocumentApp.getActiveDocument();
  let body = doc.getBody();
  let indexDoc = DocumentApp.getActiveDocument();
  let indexId = indexDoc.getId();
  let parentFolderId = DriveApp.getFileById(indexId).getParents().next().getId();
  let parentFolder = DriveApp.getFolderById(parentFolderId);
  //Logger.log(parentFolder)
  let textFolders = parentFolder.getFolders();
   while (textFolders.hasNext()) {
    let folder = textFolders.next();
    let contents = folder.getFiles();
    while (contents.hasNext()){
      let file = contents.next();
      let mime = file.getMimeType();
      //Logger.log(mime)
      //Logger.log(file.getUrl());
      if(mime === "text/plain"){
        var content = file.getBlob().getDataAsString(); 
        var contentArray = content.match(/[^\r\n]+/g);
        makeItPretty(contentArray, pdfUrl);       
      }
      if(mime === "application/pdf"){
        var pdfUrl = file.getUrl(); 
         let pdf = body.appendListItem(pdfUrl);
        pdf.setLinkUrl(pdfUrl);
      }
      //writeIndex(content, pdfUrl);
    }
    body.appendHorizontalRule();       
  }

}

function writeIndex( content, pdfUrl){
  let doc = DocumentApp.getActiveDocument();
  let body = doc.getBody();
  let add = body.appendParagraph(content);
  
  let pdf = body.appendParagraph(pdfUrl);
  pdf.setLinkUrl(pdfUrl);
  body.appendHorizontalRule()
 // Logger.log(add);
}

function testBlob(){
  let file = DriveApp.getFileById('1AY0xbOp-36k8nTCvSJcYpDIZQ21RLtpA');
  let content = file.getBlob().getDataAsString();
  let lines = content.match(/[^\r\n]+/g);
  //Logger.log(lines);
  makeItPretty(lines);
  
}

function makeItPretty(contentArray){
  let doc = DocumentApp.getActiveDocument();
  let body = doc.getBody();
  contentArray.forEach((element) => {
   //Logger.log(element)
   if (element != 'Document Information'){
     if(element.includes('http')){
       let link = body.appendListItem(element);
       link.setLinkUrl(element);
     } else {
      body.appendListItem(element);
     }
   }
  });
}