\undefinedpagestyle - r markdown won't compile to PDF if I add \usepackage{fancyhdr} and \pagestyle{fancy}

Question

I am struggling with building the basic pdf document for my thesis in markdown. It worked well, until I tried to add a header with \usepackage{fancyhdr}. Then it returns the error

! Undefined control sequence.
<argument> \undefinedpagestyle

I also realized there is no folder saying fancyhdr in the main miktex folder.

Here's my yaml header:

---
output: 
  bookdown::pdf_document2:
    toc: true
    toc_depth: 3
    number_section: true
    header-includes:
      - \usepackage{float}
      - \usepackage{fancyhdr}
      - \usepackage[margins=raggedright]{floatrow}
      - \usepackage{placeins}
      - \usepackage{chngcntr}
      - \counterwithin{figure}{section}
      - \counterwithin{table}{section}
      - \usepackage[german]{babel}
fontsize: 11pt
linestretch: 1.5
lang: de-DE
geometry: margin=2.5cm
link-citations: true
---

Here's, how I use the pagestyle in the code:

``` {r setup, include=FALSE}
library(knitr)
library(tidyverse)

opts_chunk$set(echo=FALSE)
```

\pagebreak
\pagenumbering{Roman}

\newpage
\listoffigures
\newpage
\listoftables
\newpage
\section*{Abkürzungsverzeichnis}

\pagebreak

\pagenumbering{arabic}

\pagestyle{fancy}
\fancyhead[LO,LE]{\leftmark}
\fancyfoot[CO,CE]{\thepage}

\renewcommand{\footrulewidth}{\headrulewidth}

I am quite confused about this error because my friend's file looks exactly the same regarding the fancyhdr region. He doesn't get any error.

Please help!

Answer 1

Three problems:

• the indentation of the header is wrong. header-includes can't be indented. It is not a property of pdf_document2 but needs to be at the top level

• you can't combine the floatrow and float packages

• rmarkdown automatically loads babel. You can't load it a second time with different options

---

---
output: 
  bookdown::pdf_document2:
    toc: true
    keep_tex: true
    toc_depth: 3
    number_section: true
header-includes:
  - \usepackage{fancyhdr}
  - \usepackage[margins=raggedright]{floatrow}
  - \usepackage{placeins}
  - \usepackage{chngcntr}
  - \counterwithin{figure}{section}
  - \counterwithin{table}{section}
fontsize: 11pt
linestretch: 1.5
lang: de-DE
geometry: margin=2.5cm
link-citations: true
---


``` {r setup, include=FALSE}
library(knitr)
library(tidyverse)

opts_chunk$set(echo=FALSE)
```

\pagebreak
\pagenumbering{Roman}

\newpage
\listoffigures
\newpage
\listoftables
\newpage
\section*{Abkürzungsverzeichnis}

\pagebreak

\pagenumbering{arabic}

\pagestyle{fancy}
\fancyhead[LO,LE]{\leftmark}
\fancyfoot[CO,CE]{\thepage}

\renewcommand{\footrulewidth}{\headrulewidth}

test