This might get you started. It reads the association.

Look up file type based on extension offered on the command line

use strict;
use warnings;
use Win32::TieRegistry 0.20 (Delimiter=>"/");

sub get_file_association ($) {
   my $x= shift;
   my $reg= $Registry->{"HKEY_CLASSES_ROOT/$x//"}  or return;
   # this usually refers to another entry.
   $reg &&= $Registry->{"HKEY_CLASSES_ROOT/$reg//"} if $x =~ /^\./;
   return $reg;
   }

    
# print get_file_association ('.chm');  example usage (include the dot
+)
foreach (@ARGV) {
   print $_, '=>', (get_file_association($_) || "NOT KNOWN"), "\n";
   }
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Throw-away program to find all extensions for type 'intermediate file'

#!perl -w
use strict;
use Win32::TieRegistry ( FixSzNulls => 1 );

my $Classes= $Registry->{"Classes\\"};
my @keynames= $Classes->SubKeyNames();

my @list0= grep { lc($Classes->{"$_\\"}->GetValue('')) eq 'intermediat
+e file' }  @keynames;
my (@list1, @list2);
foreach (@list0) {
   if (/^\./) {  push @list2, $_; }
   else { push @list1, $_; }
   }
my $matchexp= join ("|", map{"^\Q$_\E\$"}(@list1));
$matchexp= qr($matchexp);

push @list2, grep { /^\./ && lc($Classes->{"$_\\"}->GetValue('')) =~ /
+$matchexp/ } @keynames;

print join ("\n", @list2);
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