% Example and test for the substitutefont package:
\documentclass{article}
\usepackage{parskip}
\usepackage[LGR,T1]{fontenc}
\usepackage[colorlinks=true,linkcolor=blue,urlcolor=blue]{hyperref}
\usepackage{bookmark}
\pagestyle{empty}

% \usepackage{substitutefont} % obsolete

% Serif
\usepackage{txfontsb}
% \DeclareFontFamilySubstitution{LGR}{\rmdefault}{txrc}

% Sans
% \DeclareFontFamilySubstitution{LGR}{\sfdefault}{neohellenic}
\DeclareFontFamilySubstitution{LGR}{\sfdefault}{epigrafica}

% Monospaced
\DeclareFontFamilySubstitution{LGR}{\ttdefault}{cmtt}  % CB fonts


% Teststring
\newcommand{\alphabet}{%
  abcdefghjiklmnoprqrstuvwxyzäöüß
  {\fontencoding{LGR}\selectfont abgdezhjiklmnxoprsctufqyw} \\
  ABCDEFGHJIKLMNOPRQRSTUVWXYZÄÖÜ
  {\fontencoding{LGR}\selectfont ABGDEZHJIKLMNXOPRSTUFQYW}%
}

\begin{document}

\section*{TX fonts and Greek replacements with ``txfontsb''}

% Use Times, Helvetica, and TXTT (from the
% \href{https://ctan.org/pkg/newtx}{newtx} package) with
% \href{https://ctan.org/pkg/txfontsb}{FreeSerifb},
% \href{https://ctan.org/pkg/gfsneohellenic}{GFS Neohellenic},
% and \href{https://ctan.org/pkg/cbgreek-complete}{CB-Fonts},
% for Greek text.

\begin{description}
  \item [Normal:] \alphabet

  \item [it:] \textit{\alphabet}

  \item [sl:] \textsl{\alphabet}

  \item [bf:] \textbf{\alphabet}

  \item [bf it:] \textbf{\textit\alphabet}

  \item [sc:] \textsc{\alphabet}

  % \item [bf sc:] \textsc{\textbf\alphabet} missing in Bodoni

  \item [sf:] \textsf{\alphabet}

  \item [sf bf:] \textsf{\textbf\alphabet}
  
  % \item [sf sl:] \textsf{\textsl\alphabet}
  % 
  % \item [sf sc:] \textsf{\textsc\alphabet}

  \item [tt:] \texttt{\alphabet}

  % \item [tt bf:] \texttt{\textbf\alphabet}

\end{description}

\end{document}