hmm, something could be done using Dirplus, and one of the time UDF's.

Here is something using flipctime() just because i know that one
Code:
$files = dirplus("c:\pdf files",'/a-d /f pdf')

$startdate = '2005/12/01'
$endDate = '2006/1/01'


for each $file in $files
	;change the time to 24h
	$time = timeconvert(split($file.DateLastModified)[1] + split($file.DateLastModified)[2])

	;reset date to yyyy/MM/DD
	$date = split($file.DateLastModified)[0]
	$date = split($date,'/')
	$date = $date[2]+'/'+$date[0]+'/'+$date[1]

	$filedate = flipctime($date, $time)
	if $filedate > flipctime($startDate,'00:00') and $filedate < flipctime($enddate,'00:00')
		? $file
	endif
next


grab the UDFs timeconvert, dirplus, and flipctime...