title: font change for chapter, section, subsection titles
body: <p>So, i am struggling to change the font for title/section/subsection in latex. </p>
  
  <p>Here is my code : </p>
  
  <pre><code>% !TEX TS?program = pdflatexmk
  
  \documentclass[fontsize=12pt]{book}
  
  \usepackage[T1]{fontenc}
  
  \usepackage{amsmath}
  
  \usepackage{mathpazo}
  
  %changing font of section/chapter title
  \usepackage{fontspec}
  \usepackage{titlesec}
  \newfontfamily\headingfont{Papyrus}
  \titleformat{\chapter}{\LARGE\headingfont}
  \titleformat{\section}{\LARGE\headingfont}
  \titleformat{\subsection}{\Large\headingfont}
  \titleformat{\subsubsection}{\large\headingfont}
  
  
  
  \title{my report}
  \author{user name}
  \date
  
  
  \linespread{1.5}
  
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  \begin{document}
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  \maketitle
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  \tableofcontents
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  \chapter{introduction}
  text : intro
  \section{first section}
  text :  section
  \subsection{this subsection}
  text :section
  \subsubsection{this and that subsection}
  text :subsub
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  \end{document}
  </code></pre>
  
  <p>And this is the output: 
  <a href="https://i.stack.imgur.com/tq4UM.png" rel="noreferrer"><img src="https://i.stack.imgur.com/tq4UM.png" alt="enter image description here"></a>
  The font is only implemented in the <code>chapter</code> and <code>subsection</code>. Not for others. 
  And also the numbering is lost. For example, without <code>titlesec</code>and <code>fontspec</code> this is what it looks like. The chapter and subsection numbering is lost with that. 
  I cant find the bug. (also kind of annoying to use fontspec as it could not find the default latex font, so had to copy paste the <code>otf</code> file in the working directory)</p>
  
  <p><a href="https://i.stack.imgur.com/oefJC.png" rel="noreferrer"><img src="https://i.stack.imgur.com/oefJC.png" alt="enter image description here"></a></p>