I found a solution for associating the FDF with a PDF file:

package PDF::FDF::Simplemod;
use PDF::FDF::Simple;
our @ISA = qw(PDF::FDF::Simple);

sub _fdf_header {
  my $self = shift;
  return <<__EOT__;
%FDF-1.2

1 0 obj
<<
/FDF << /Fields 
[
__EOT__
}

sub _fdf_footer {
  my $self = shift;
  return <<__EOT__;
]
/F (test.pdf)/ID [ <id string 1><id sring 2>
] >> 
>> 
endobj
trailer
<<
/Root 1 0 R

>>
%%EOF
__EOT__
}
1;
[download]

Part of the problem seemed to be that the FDF Simple module was generating FDF headers that weren't compatible with my verison of Acrobat (5.0.5). So I generated an FDF from the PDF form so I could determine the format for the headers.