I want to knit a pdf-document but the keywords don't appear in the final document. Can someone say me what I'm doing wrong?

```
---
title: "title"
subtitle: "subtitle"
author: "author"
date: "09 04 2019"
output:
  pdf_document:
keywords: "word1, word2, word3"
footerdate: yes
abstract: 'Insert abstract here'
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

# Introduction

```

[![enter image description here](https://i.stack.imgur.com/G6PFw.png)](https://i.stack.imgur.com/G6PFw.png)