How to change font for a TextField with pdfLaTeX?

Question

First of all, I am a TeX-Noob, so this may be easy answered by a pro ;-)

We have MiKTeX 2.9 and pdfLaTeX for creating pdf documents.

One pdf document contains multiple form fields (TextField), and one specific form field has to be a barcode. A code39.ttf font is installed in the system.

\documentclass[ngerman,oneside]{scrreprt}
\usepackage{xcolor}
\setlength\paperheight{55mm}
\setlength\paperwidth{85mm}
\usepackage[left=0mm,top=0mm,bottom=0mm,right=0mm]{geometry}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{textcomp}
\renewcommand{\familydefault}{phv}
\newcommand{\transparentTextfield}[2]{\TextField[backgroundcolor={}, bordercolor={}, charsize=14pt, width=#1 ,height=6mm, name=#2]{}}
\usepackage{graphicx}
\usepackage[pdftex,a4paper=true,colorlinks=true,pdftitle={Title},pdfsubject={Subject},pdfauthor={Me},pdfpagemode=UseNone,pdfstartview=FitH,pagebackref,pdfhighlight={/N}]{hyperref}
\begin{document}
\begin{Form}
\begin{picture}(0,0)

\setlength{\unitlength}{1mm} 

\put(2,-10){\TextField[backgroundcolor={}, bordercolor={}, charsize=0pt, width=73mm, height=7mm, name=barcode1]{}}
\put(6.5,-46){\TextField[backgroundcolor={}, bordercolor={}, charsize=8pt, width=12mm ,height=5mm, name=number1]{}}
\put(38,-46){\TextField[backgroundcolor={}, bordercolor={}, charsize=8pt, width=25mm ,height=5mm, name=number2]{}}

\end{picture}
\end{Form}
\end{document}

But how can I set the font of the TextField to my installed code39 font?

My workaround is as follows: After creating the pdf, I open it with Acrobat Professional and change the font of the text field to Code39 manually and save it.