\documentclass{article}

\usepackage{filecontents,datatool}
% Set up your database of mail merge content (in CSV)
\begin{filecontents*}{mail_merge.csv}
letternum, fromperson, toperson, toaddress
1, Monster Mania Building Corp, John Doe, PO Box 1000 \\ {Athens, AK 11111}
2, Jane Doe, Rumplestiltskin, Castle ABC \\ {Neverland, NL 54321}
\end{filecontents*}

\usepackage{lipsum}% Just for this example
\sloppy% Just for this example

% Set up your document layout
\usepackage[margin=1in,left=2in,includeheadfoot]{geometry}
\usepackage{eso-pic}% Used to place the page number

\setlength{\parindent}{0pt}% Remove paragraph indent
\setlength{\parskip}{1\baselineskip plus 2pt minus 1pt}% Big skip between paragraphs

% Placement of the page number...
\AddToShipoutPictureFG{%
  \AtTextUpperLeft{%
    \ifnum\value{page}>1 % ...only on pages 2, 3, ...
      \raisebox{-.85\baselineskip}{\makebox[0pt][r]{%
        \begin{tabular}[t]{ l @{} }
          Page \thepage \\
          abc \\
          def
        \end{tabular}~~~}}%
    \fi
  }%
}
\pagestyle{empty}% Don't place anything in the header/footer

% Load the mail merge database
\DTLloaddb[keys={letternum,fromperson,toperson,toaddress}]{mailmerge}{mail_merge.csv}

% Extract a record of choice...
\DTLassign{mailmerge}{1}% ... like record 2 in this case
  {\letternum=letternum,\fromperson=fromperson,\toperson=toperson,\toaddress=toaddress}

\begin{document}

\makebox[0pt][r]{%
  \smash{\begin{tabular}[t]{ p{5em} @{} }
    \raggedleft\fromperson
  \end{tabular}~~~}}%
\today

\bigskip

\begin{tabular}{@{} l}
  \toperson \\
  \toaddress
\end{tabular}

\bigskip

Dear Sir or Madam:

\bigskip

\lipsum[1-6]

\bigskip

Regards,

\vspace{4\baselineskip}

\fromperson

\end{document}