\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{graphicx} 
\usepackage{caption,subcaption}
\usepackage{lscape}
\usepackage{tabularx}
\begin{document}
\pagenumbering{gobble}
\begin{landscape}
\begin{figure}
     \centering
     \begin{subfigure}[b]{0.5\textwidth}
         \centering
         \includegraphics[width=\textwidth]{Change_foreign_citizens_Romania.pdf}

         \label{fig 1}
     \end{subfigure}
     \hfill
     \begin{subfigure}[b]{0.5\textwidth}
         \centering
         \includegraphics[width=\textwidth]{Change_foreign_citizens_Morocco.pdf}

         \label{fig 2}
     \end{subfigure}
     \hfill
     \begin{subfigure}[b]{0.5\textwidth}
         \centering
         \includegraphics[width=\textwidth]{Change_foreign_citizens_Syria.pdf}

         \label{fig 3}
     \end{subfigure}
        
\medskip

     \centering
     \begin{subfigure}[b]{0.5\textwidth}
         \centering
         \includegraphics[width=\textwidth]{Change_foreign_citizens_Poland.pdf}

         \label{fig 4}
     \end{subfigure}
     \hfill
     \begin{subfigure}[b]{0.5\textwidth}
         \centering
         \includegraphics[width=\textwidth]{Change_foreign_citizens_China.pdf}

         \label{fig 5}
     \end{subfigure}
     \hfill
     \begin{subfigure}[b]{0.5\textwidth}
         \centering
         \includegraphics[width=\textwidth]{Change_foreign_citizens_Bulgaria.pdf}

         \label{fig 6}
     \end{subfigure}
     
\medskip

     \centering
     \begin{subfigure}[b]{0.5\textwidth}
         \centering
         \includegraphics[width=\textwidth]{Change_foreign_citizens_Ukraine.pdf}

         \label{fig 7}
     \end{subfigure}
     \hfill
     \begin{subfigure}[b]{0.5\textwidth}
         \centering
         \includegraphics[width=\textwidth]{Change_foreign_citizens_Albania.pdf}

         \label{fig 8}
     \end{subfigure}
     \hfill
     \begin{subfigure}[b]{0.5\textwidth}
         \centering
         \includegraphics[width=\textwidth]{Change_foreign_citizens_Russia.pdf}

         \label{fig 9}
     \end{subfigure}
        

\end{figure}
\end{landscape}
\end{document}

