The proper keys for pdf_get_parameter and pdf_get_value are under "Parameters and Values" under "A PDFlib Quick Reference" in the PDFlib reference manual (google is your friend).
To get the font name:
$fontname = pdf_get_parameter($pdf, "fontname", 0);
To get the font size:
$size = pdf_get_value($pdf, "fontsize", 0);
PDF_get_minorversion