Add example of how adding pre generated pdfs works

book/book.tex

@@ -56,6 +56,11 @@ produce a lot of \ch{CO2}.
 \end{center}
 \end{figure}
 
+\begin{figure}[!htb]
+  \includegraphics{figures/fig-life-planet-sourdough-timeline-external.pdf}
+  \caption{Embedding pre generated pdf works}
+\end{figure}
+
 \begin{figure}[!htb]
   \includegraphics[width=\textwidth]{baking-experiment-temperatures.png}
   \caption[Surface temperature for different steaming methods]{png file}