yes. i have merged pdf's. Get the fpdf and fpdi libraries and put them in to the code igniter third party folder. then it is just a matter of reading the manual for fpdfi and merging the documents. use this to set up the libraries
require_once("application/third_party/fpdf/fpdf.php");//http://www.fpdf.org/
require_once("application/third_party/fpdi/FPDI_Protection.php");//http://www.setasign.de/products/pdf-php-solutions/fpdi/
then this snippet of code should give you an idea of how it works. note i have edited sections of this for clarity. this example streams the pdf file. you could just as easily save the file elsewhere.
$files = array(<file full paths here>);
$pdf = new FPDI_Protection();
if ($data->password)
{
$pdf->setProtection(array(),$data->password);
}
for ($i = 0; $i < count($files); $i++ )
{
$pagecount = $pdf->setSourceFile($files[$i]);
for($j = 0; $j < $pagecount ; $j++)
{
$tplidx = $pdf->importPage(($j +1), '/MediaBox'); // template index.
$pdf->addPage('L','A4');// orientation can be P|L
$pdf->useTemplate($tplidx, 0, 0, 0, 0, TRUE);
}
unlink($files[$i]); // you may not want to unlink the files!
}
$dt = new DateTime(NULL, new DateTimeZone($data->user->timezone));
// set the metadata.
$pdf->SetAuthor($data->user->user_name);
$pdf->SetCreator('website name!');
$pdf->SetTitle('PDF, created: '.$dt->format(MYHMRS_DATETIME_FRIENDLY));
$pdf->SetSubject('PDF subject !');
$pdf->SetKeywords('website name!'.", keywords! ".$data->user->user_name);
$output = $pdf->Output('', 'S');
$name = "PDF".'-'.$dt->format('ymd').'.pdf';
$this->output
->set_header("Content-Disposition: filename=$name;")
->set_content_type('Application/pdf')
->set_output($output);
as for getting pdfs from other sites, firstly make sure you are allowed to do this, then it is matter of using cURL. (copy URL). there is a codeigniter library to do this, or you can use the PHP library.