[Tex/LaTex] How to change LaTeX Font Style

Question

How do I change the font in LaTeX?

I want to create font that looks like this:

but TeXShop gives me this font:

How do I can make the font in the bottom image look like the font in the top image? The text looks a bit thicker and darker than the first text.

The second paragraph was produced by:

\documentclass[12pt]{article}

\usepackage[ left = 23mm, right  = 23mm, top = 24mm, bottom = 24mm ] {geometry}
\usepackage{mathtools}
\usepackage{graphicx}
\usepackage{pgfgantt}
\usepackage{tikz}
\usetikzlibrary{positioning}
\usetikzlibrary{arrows,matrix}
\usepackage{amssymb, amsmath, mathptmx}
\usepackage{pstricks, pst-node, pst-plot, pst-circ}
\usepackage{moredefs}
\usepackage{verbatim}
\usepackage{subcaption}
\interlinepenalty=10000

\begin{document}
\begin{titlepage}
\noindent
This is a simple and traditional approach involving storage of the piece positions, in 
a 64-bit word, to represent each of the 64 positions on the chess board. Representing a 
piece on the board implies turning on that bit. There are 12 bit-boards to encode the 
6 white and 6 black pieces (king, queen, rook, bishop, knight, pawn). Figure 2.6 
illustrates the bit-board of the white queen corresponding to the position h5.
\end{titlepage}
\end{document}

Answer 1

CW from the comments:

Instead of

\usepackage{amssymb, amsmath, mathptmx}

(mathptmx is a Times clone), use

\usepackage{amssymb, amsmath, lmodern}

(lmodern is an updated Computer Modern).

\documentclass[12pt]{article}
\usepackage{amssymb, amsmath, lmodern}

\begin{document}
\noindent This is a simple and traditional approach involving storage of the piece positions, in 
a 64-bit word, to represent each of the 64 positions on the chess board. Representing a 
piece on the board implies turning on that bit. There are 12 bit-boards to encode the 
6 white and 6 black pieces (king, queen, rook, bishop, knight, pawn). Figure 2.6 
illustrates the bit-board of the white queen corresponding to the position h5.
\end{document}