If you are using the PDFLib Lite version, this function will not work. You have to purchase the full version of PDFLib
(PECL pdflib >= 2.1.0)
PDF_open_pdi_document — Prepare a pdi document
$p
, string $filename
, string $optlist
) : intOpen a disk-based or virtual PDF document and prepare it for later use.
If you are using the PDFLib Lite version, this function will not work. You have to purchase the full version of PDFLib