I want to use a combination of fonts I saw here but I don't know how to install them correctly. I tried running the code in the answer but I get an error saying mathpazo is unknown. Up until now I've only used the default font so I have no experience with this topic. I'm using Texmaker and Windows. Any help is appreciated :)
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[tracking]{microtype}
\usepackage[sc,osf]{mathpazo} % With old-style figures and real smallcaps.
\linespread{1.025} % Palatino leads a little more leading
% Euler for math and numbers
\usepackage[euler-digits,small]{eulervm}
\AtBeginDocument{\renewcommand{\hbar}{\hslash}}
\usepackage{ntheorem}
% No easy way of putting the theorem description in italics?
% It seems I need to define a new style...
\makeatletter
\newtheoremstyle{mystyle}%
{\item[\hskip\labelsep \theorem@headerfont ##1\ ##2\theorem@separator]}%
{\item[\hskip\labelsep \theorem@headerfont ##1\ ##2\ \textit{(##3)}\theorem@separator]}
\makeatother
\theoremstyle{mystyle}
\theoremheaderfont{\scshape}
\theorembodyfont{\upshape}
\newtheorem{theorem}{theorem}
\usepackage{amsmath}
\DeclareMathOperator{\Res}{Res}
\begin{document}\pagestyle{empty}
\begin{theorem}[Residue Theorem]
Let $f$ be analytic in the region $G$ except for the isolated
singularities $a_1,a_2,\dots,a_m$. If $\gamma$ is a closed
rectifiable curve in $G$ which does not pass through any of the
points $a_k$ and if $\gamma\approx 0$ in $G$, then
\[
\frac{1}{2\pi i}\int_\gamma\! f = \sum_{k=1}^m
n(\gamma;a_k)\Res(f;a_k)\,.
\]
\end{theorem}
\end{document}
mathpazois installed? If not, the first thing to do is certainly to install it, which you could do manually in the MiKTeX Console. Then you might have to "Refresh font map files", which is under the "Tasks" menu. – Vincent Dec 17 '19 at 02:15