Is this "specific place" in the HTML file between two lines? If if is, you could do something like this: 
open(HTML,"<$html_file") || die "Could not open $html_file:$!\n";
open(TXT,"<$txt_file") || die "Could not open $txt_file:$!\n";
open(OUT,">$output_file) || die "Could not open $ouput_file:$!\n";

while (<HTML>) {
   print OUT $_;
   if (/this is how you recognise the specific point/) {
      while (<TXT>) {
        print OUT $_;
      }
   }
}

[download]
If you need to replace something (like a custom tag) in the HTML file with the contents of the TXT file, that's a somewhat different story. If you expect the text file to be short, you could just slurp it into a text variable with $txt=join("",<TXT>); and then, at the appropriate point in the loop copying HTML to the output file, you could to a s/<custom tag>/$txt/;

In reply to Re: Adding contents of a file into another by matija
in thread Adding contents of a file into another by Gbuk

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