Error: LaTeX Error: Missing \begin{document} - latex

Question

I am a beginner in R and I need to export R markdown file into pdf. I downloaded MikTex, TexStudio and uploaded the package tinytex. I tried to plug the code \begin{document} but it doesn't seem to be working, so I am not sure if I am plugging it in the right space.
output:
pdf_document:
fig_caption: yes
fig_height: 6
fig_width: 7
number_sections: yes
toc: yes
toc_depth: 3
html_document: default
word_document:
toc: yes
toc_depth: '3'
header-includes: |
```{=latex}
\usepackage{fvextra}
\begin{document}
\DefineVerbatimEnvironment{Highlighting}{Verbatim}{
showspaces = false,
showtabs = false,
breaklines,
commandchars=\\\{\}
always_allow_html: yes

Answer 1

There are a couple of syntax errors:
output: should not be indented. This is a parent key for pdf_document: etc.
\DefineVerbatimEnvironment{Highlighting}{Verbatim}{ is missing the closing }
you don't actually need to escape to raw latex in the header-includes:
Don't use \begin{document} in the preamble.
"I downloaded [...] TexStudio" -> TeXstudio is not really great for editing rmd files. I suggest to have a look at Rstudio instead.
---
output:
pdf_document:
fig_caption: yes
fig_height: 6
fig_width: 7
number_sections: yes
toc: yes
toc_depth: 3
keep_tex: true
html_document: default
word_document:
toc: yes
toc_depth: '3'
header-includes: |
\usepackage{fvextra}
\DefineVerbatimEnvironment{Highlighting}{Verbatim}{
showspaces = false,
showtabs = false,
breaklines,
commandchars=\\\{\}
}
always_allow_html: yes
---
test