My first guess is that the string you put togther for $cmd is not being interpreted right by pdftohtml, and is just quickly failing. It's not that it isn't waiting. Try something like this instead: (experiment around till it works) :-)

#my $cmd = 'pdftohtml ' . $filename_pdf . ' ' . $filename_html . ' -no
+f
#+rames -c -i >/dev/null' ;
#system("$cmd");

my @args = ( $filename_pdf, $filename_html, 'noframes', '-c-, '-i' , '
+>', '/dev/null' );
system ('pdftohtml', @args);
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Sometimes programs want '>', '/dev/null' , separated. Others might want '> /dev/null' as a single string. Try some variations in the @arg list until you get the desired output. I remember one tricky program I had, that wouldn't accept @args like '-o', "$filename", but needed "-o $filename".... took me all day to figure it out by trial and error. :-)

UPDATE It was pointed out to me that the /dev/null redirection, may be nonsense, in this particular instance. It didn't make much sense to me either, when I first saw it, but I have seen other apps, like mplayer or mencoder, which required the following odd redirection

$pid = open(MP, "| mplayer @options  init.mpg >/dev/null 2>&1 ");
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