I usually provide registration forms for our workshops in pdf format and also latex code to fill in data: Let us first have a sample Registration form (paper size-letterpaper):
First page (form-0):

Second page (form-1):

Now the code:
\documentclass[letterpaper]{article}% ensure identical page size
\usepackage[charter]{mathdesign}
\usepackage[svgnames]{xcolor}
\usepackage{tikz}
\usepackage[linkbordercolor={0 0 0},colorlinks=true,linkcolor=magenta]{hyperref}
\newcommand{\setfont}[2]{{\fontfamily{#1}\selectfont #2}}
\newcommand{\mycolor}[1]{\color{NavyBlue}{#1}}
\pagestyle{empty}
\begin{document}
% Page 1
\begin{tikzpicture}[remember picture,overlay]
\node at (current page.center) {\includegraphics{form}};
\begin{scope}[shift={(current page.south west)},every node/.style={anchor=base west}]
% Grid to help find the positions (remove in final version)
\draw [help lines,xstep=.2,ystep=.2,very thin] (0,0) grid (current page.north east); % if you want finer grid
\draw [help lines,xstep=1,ystep=1,thick] (0,0) grid (current page.north east);
\draw [help lines,very thick] (0,0) grid [step=5cm] (current page.north east);
\foreach \x in {0,...,21} { \node [anchor=north] at (\x,1) {\x}; }
\foreach \y in {0,1,...,27} { \node [anchor=east] at (1,\y) {\y}; }
% Comment up to here in final version
\node at (8.5cm,21.79cm) {\mycolor{\textbf{\vrule width 12pt height 1.5pt\hspace{.08cm} \vrule width 12pt height 1.5pt \,\, Harish Kumar}}};
\node at (7.8cm,20.93cm) {\mycolor{\textbf{Degree}}};
\node at (7.8cm,20.1cm) {\mycolor{\textbf{Designation, Department}}};
\node at (7.8cm,19.27cm) {\mycolor{\textbf{XX years}}};
\node at (7.8cm,18.43cm) {\mycolor{\textbf{XXXXX XXXXX}}};
\node at (7.8cm,17.61cm) {{\textbf{\href{mailto:yourmail@something.com}{\texttt{yourmail@something.com}}}}};
\node at (7.8cm,16.8cm) {\mycolor{\textbf{Dr. Harish Kumar}}};
\node at (7.8cm,15.95cm) {\mycolor{\textbf{Designation, Department}}};
\node at (7.8cm,15.13cm) {\mycolor{\textbf{Institute}}};
\node at (7.8cm,14.3cm) {\mycolor{\textbf{XXX XXX}}};
\node at (8.5cm,13.5cm) {\mycolor{\textbf{$\checkmark\,\,\,\quad$ \vrule width 12pt height 2pt }}};
\node at (8.87cm,12.69cm) {\mycolor{\textbf{\vrule width 12pt height 2pt $\quad\,\,\,\checkmark$}}};
\node at (3.7cm,11.83cm) {\mycolor{\textbf{XXXXX}}};\node at (12.2cm,11.83cm) {\mycolor{\textbf{\today}}};
\node at (3.7cm,11cm) {\mycolor{\textbf{Your Bank}}}; \node at (12.3cm,11cm) {\mycolor{\textbf{Here}}};
\node at (15.4cm,9cm) {\setfont{frc}{\color{Blue}{Harish Kumar}}};
\end{scope}
\end{tikzpicture}
\clearpage
% Page 2
\begin{tikzpicture}[remember picture,overlay]
\node at (current page.center) {\includegraphics{form}};
\begin{scope}[shift={(current page.south west)},every node/.style={anchor=base west}]
% Grid to help find the positions (remove in final version)
\draw [help lines] (0,0) grid (current page.north east);
\draw [help lines,thick] (0,0) grid [step=5cm] (current page.north east);
\foreach \x in {0,...,21} { \node [anchor=north] at (\x,1) {\x}; }
\foreach \y in {0,1,...,27} { \node [anchor=east] at (1,\y) {\y}; }
% Comment up to here in final version
%
\node at (3.4cm,21.64cm) {{\mycolor{PEC}}};
\node at (3.4cm,20.8cm) {{\mycolor{\today}}};
\node at (15.9cm,19.55cm) {\setfont{frc}{\color{Blue}{Harish Kumar}}};
\node at (5.68cm,16.74cm) {\vrule width 12pt height 1pt \hspace{.08cm} \vrule width 12pt height 1pt \hspace{.2cm} \setfont{pzc}{\mycolor{\Large Harish Kumar}}};
\end{scope}
\end{tikzpicture}
\clearpage
\end{document}
You get this:

Grid is provided just for making it easy to locate the exact coordinates. In the final form comment these lines:
\draw [help lines] (0,0) grid (current page.north east);
\draw [help lines,thick] (0,0) grid [step=5cm] (current page.north east);
\foreach \x in {0,...,21} { \node [anchor=north] at (\x,1) {\x}; }
\foreach \y in {0,1,...,27} { \node [anchor=east] at (1,\y) {\y}; }
% Comment up to here in final version
to get:

Note: The blank form which I used above is typeset on letterpaper. Hence in the tex code, I have used the same size. Use appropriate paper size in your tex code ( same as your pre-printed paper).
I have a pre printed paper (I am able to fill the form by hand). But I want to fill it with my printer... In @Harish Kumar's answer I can see how to place a specific field anywhere I want.
For example: I need to configure the generated pdf to be 10cm x 5cm (real size of paper)
– Mateo Torres Feb 25 '14 at 20:12