That depends .... how is it encoded?
Basically, the procedure would be something like:

#!/usr/bin/perl -w
use strict;
use warnings;

[code to open database]

sub decode {
    my $encoded_data = shift;
    [code to decode $encoded_data to $decoded_data]
    return $decoded_data;
}

my $blob;
[code to get column from database and put into $blob]
my $pdf = &decode($blob);
open(OUT_PDF, ">DOCUMENT.PDF") or die "Can't open file!";
print OUT_PDF $pdf;
close(OUT_PDF);
[download]

The chunks in the square brackets are the bits of Perl code that I can't specify because you didn't give enough clues.

For the first one, you need to get access to your database. In the Perl community, it seems that the DBI package is the most popular (it's what I use). I don't know anything about DBISAM, so I don't know if there's a DBI driver module available for it. If not, then you could use the ODBC driver (again, that's what I usually use), providing you have an ODBC driver for your database.

For the second item (the decode function), I can't help you with that as you haven't told me anything about the encoding scheme. If you know the encoding scheme, look on CPAN for a module that will decode the appropriate scheme, and plug in the appropriate code.

In the final chunk, if you used DBI, you could use something like this:

my $STH = $DBH->execute("SELECT [column] "
.                       "FROM [table] "
.                       "WHERE [condition]")
or die "WTF?  I can't find what you're looking for!";
my $array_ref = $STH->fetchrow_arrayref;
$blob = $array_ref->[0];
[download]

Of course, there are now a few new blanks to fill in which you'll have to determine, because you didn't say.

--roboticus