This information is, at least for the case of Word, provided by the MS Word Object Model. For the other cases, I don't know, especially for the .pdf files, as I don't know whether Acrobat Reader provides an OLE interface to the application and its document. The best way in my opinion is still to print the documents to a printer and then count the pages of the output. That printer does not necessarily need to be a real paper printer, but for example a .pdf printer, if you know how to get the number of pages in a PDF file.

For printing any document under Windows, take a look at the shell commands provided in the registry of Explorer and/or at the facilities for automating (Office) applications provided by Win32::OLE. For getting the count of pages out of a PDF, I would look at the (various) PDF modules that CPAN provides.

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web
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perl -ne 'undef $/; $\="\n"; 
(($count = $1) =~ s/.*\Count\s*(\d+).*/\1/ && 
$pages < $count ? $pages=$1 : 1) 
while s/(<<[^<]*\/Type\s*\/Pages[^>]*>>)//; 
print $pages' somefile.pdf
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I tested it one some pdf files and it seems to work. It is not a very elegant solutions and might be heavy for large files. It reads out the sections like the following in the PDF file and assumes that the larges count holds the number of pages, which is really an assumption.

23 0 obj
<< /Type /Pages
   /Resources 76 0 R
   /MediaBox [ 0 0 595 842 ]
   /Kids [ 24 0 R
            // and so on
           ]
   /Count 11
>>
endobj
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- wine

I don't know exactly, but in another node it said that PDF format files have a basis in postscript. You may want to look in that direction for information on getting the page count with that format. Hope that helps a little.

If you're on Win and have Word installed you can use Win32::OLE as Corion indicated above.

Below is a working example

#!perl -w

use strict;

use Win32::OLE;
use Win32::OLE::Const;
use Win32::OLE::Variant;

## Start Word engine
my $Word = Win32::OLE->new('Word.Application', 'Quit');
$Word->{'DisplayAlerts'} = 0;
my $wdc = Win32::OLE::Const->Load("Microsoft Word");

my $tpl = "c:\\perltest\\pages.doc"; ## Subject to change

## Open template
my $doc = $Word->Documents->Open($tpl, {ReadOnly =>  Variant(VT_BOOL, 
+1) } ) || die"add";

my $pages = $Word->ActiveDocument->BuiltInDocumentProperties( $wdc->{w
+dPropertyPages} )->Value;

$doc->Close( { SaveChanges => $wdc->{wdDoNotSaveChanges} } );

print " $tpl contains $pages pages\n";
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