为什么我不能使用 overleaf 中的壁纸包将 pdf 用作背景？

Question

我想在证书页面上使用我的学院信头，但我无法在背面这样做，而且它也没有给出任何错误。

\documentclass[a4paper,12pt]{report}
\usepackage{graphicx}      %package for using images
\usepackage[a4paper, margin = 1in]{geometry}
\usepackage{anyfontsize}
\usepackage{fancyhdr}      %package for header and footer
\usepackage{caption}
\usepackage{tocloft}   
\usepackage{titlesec}
\usepackage[hidelinks]{hyperref}   
\usepackage{times}       %for using times new roman font
\usepackage{romannum}
\usepackage{amsmath}
\usepackage{float}
\usepackage{wallpaper}

\begin{document}
\newpage
\fancypagestyle{certificate}{
\fancyhf{}
\cfoot{}
\chead{}
\rhead{}
\renewcommand{\headrulewidth}{0pt}
}
\thispagestyle{certificate}
\ThisURCornerWallPaper{0.96}{letter_head_MS_thesis.pdf}
\vspace*{1cm}
\begin{center}
\fontsize{20pt}{16pt}\selectfont{\textbf{CERTIFICATE}}
\end{center}
\phantomsection
\addcontentsline{toc}{chapter}{Certificate}
\vspace{1cm}

 This is to certify that -Student-Name-, BS-MS (Dual Degree) student in
Department of -Discipline-, has completed bonafide work on the dissertation entitled `-MS-Thesis-Title-' under my supervision and guidance.

\vspace{4cm}
\noindent
\hspace{1cm}
\begin{minipage}[t]{2in}
 April 2019\\
IISER Bhopal
\end{minipage}
\hfill
\begin{minipage}[t]{2.7in}\centering
\hspace{3cm}\\        %in pdf here will be space for your sign
-your prof. name-     %remove this with "-" and write your prof. name 
\end{minipage}

\vspace{4cm}
\noindent
\vspace{3cm}
\begin{minipage}[l]{2in}\centering
Committee Member\\
\vspace{0.5cm}
\underline{\hspace{5cm}}\\
\vspace{0.7cm}
\underline{\hspace{5cm}}\\
\vspace{0.7cm}
\underline{\hspace{5cm}}
\end{minipage}
\hfill
\begin{minipage}[c]{2in}\centering
Signature\\
\vspace{0.5cm}
\underline{\hspace{4cm}}\\
\vspace{0.7cm}
\underline{\hspace{4cm}}\\
\vspace{0.7cm}
\underline{\hspace{4cm}}
\end{minipage}
\hfill
\begin{minipage}[r]{1.5in}\centering
Date\\
\vspace{0.5cm}
\underline{\hspace{4cm}}\\
\vspace{0.7cm}
\underline{\hspace{4cm}}\\
\vspace{0.7cm}
\underline{\hspace{4cm}}
\end{minipage}
\end{document}

我在这里附上了 MWE，请帮帮我。我的朋友在 TexStudio 中得到了结果，但我在 overleaf 中没有得到相同的结果。