Not much documentation except the latest Pdflib manual, but either way the textlen is not required.
I have this and it works for me:
$opts = "fontname={$this->font[0]->_name} fontsize=$font_size encoding=$font_encoding alignment=$align ";
if ($indent) {
$opts .= "leftindent=$indent ";
}
$textflow = pdf_create_textflow($this->_pdf,$data,$opts);
I've been working with the pdflib v7 for 2 months now, and since there's virtually no documentation on anythign except their manual, I recommend reading it. It's pretty good and detailed.