documentclass{article}
usepackage{multirow}
setlengthparindent{0pt}
usepackage{geometry}
usepackage{longtable}
usepackage{float}
usepackage{verbatim}
usepackage{hyperref}
geometry{left=1.5cm,right=1.5cm,top=1.5cm,bottom=1.5cm}

title{Docx from tex file example}

begin{document}

maketitle

<<chunk1,echo=TRUE,message=FALSE>>=
library(survival)

str(lung)
@

end{document}

path/to/pandoc/pandoc -o min_reproducible_example.docx min_reproducible_example.tex

Error at "source" (line 68, column 67):
unexpected end of input
definecolor{shadecolor}{rgb}{0.969, 0.969, 0.969}color{fgcolor}begin{kframe}

Warning message:
In shell(command) :
  '"C:/pandoc/pandoc" -o min_reproducible_example.docx min_reproducible_example.tex --default-image-extension=png' execution failed with error code 65