Many functions in the native ClibPDF and the PHP module, as well as in PDFlib, have the same name.
ClibPDF lets you create PDF documents with PHP. It is available at FastIO but it isn't free software. You should definitely read the licence before you start playing with ClibPDF. If you cannot fullfil the licence agreement consider using pdflib by Thomas Merz, which is also very powerful. ClibPDF functionality and API is similar to Thomas Merz's pdflib but, according to FastIO, ClibPDF is faster and creates smaller documents. This may have changed with the new version 2.0 of pdflib. A simple benchmark (the pdfclock.c example from pdflib 2.0 turned into a php script) actually shows no difference in speed at all. The file size is also similar if compression is turned off. So, try them both and see which one does the job for you.