Add the hyperref package

letter.tex

@@ -3,6 +3,7 @@
 \usepackage[top=1.5cm]{geometry}
 \usepackage{tikz}
 \usepackage{tikzpagenodes}
+\usepackage{hyperref}
 
 \signature{\vspace{-1.5cm}NAME HERE}
 \address{\vspace{2cm} \\ Computer \& Information Sciences \\ University of Strathclyde \\ Livingstone Tower \\ 26 Richmond Street \\ Glasgow \\ G1 1XH}